Disclaimer: I don't own anything about Harry Potter, JKR does though.
The First Prophecy
Divination was one of the most unreliable branches of magic, which was widely known. Indeed, many wizards nowadays weren't even sure if there actually were any real prophecies or if the correct prophecies weren't perhaps just based on careful observation and mysterious demeanour of the seer.
Albus Dumbledore who was currently heading down the road to Hogsmeade was more inclined to agree with the later. He had studied many branches of magic and was even considered an expert in many, but he had yet to find prove for real prophesies. Granted, there were more things on this world than wizard kind would probably ever know, but still.
In fact, the only reason why he was heading for the Hog's Head was because he had been too polite to refuse the candidate for the vacant post of the divination teacher an interview before discontinuing the subject at Hogwarts. Well, and because he had felt some pity for the poor woman. That she had been only able to get a room at the Hog's Head was indication of the low funds of famous Cassandra Trelawney's great-great-granddaughter.
The Headmaster already dreaded the moment he would inevitably have to tell her that he would not hire her. He could simply see no point in teaching such a subject to his students even if just as an electable. Hogwarts had to uphold a reputation as the world's best school for young wizards and witches and he wanted to emphasise the subjects most useful in later life and frankly, no one actually used divination.
So it was with some apprehension that he went to the pub's door and asked for a Sybill Trelawney. He was directed to the shabbiest room this place could offer, further support to his suspicion regarding the young woman's situation.
"Hello Professor, so nice to finally see you in person. I had already seen your arrival, of course. The Inner Eye Sees.", declared Sybill Trelawney with an overly dramatic air.
Oh my, Albus Dumbledore thought and suppressed a sigh. He took in the way she had dressed herself, a very obvious attempt to look the accomplished Seer. Unfortunately, the effect was a rather ridiculous appearance reminding him of an insect wearing many shawls and beads.
He shook his head slightly to clear it, he really didn't want to be prejudiced against the poor woman just based on her questionable fashion sense.
"Good morning, Ms Trelawney", he said, "It is my pleasure to meet you. Of course, I still have your school records, so I already saw you were an excellent student in this subject. If you were so kind as to tell me about your experiences after graduating Hogwarts…" he looked expectantly at her.
Sybill Trelawney did so most eagerly, telling him of the small fortune telling business she had built up herself. He had heard of that one, mostly that prophecies she had made there were utterly false and the ones that were right probably only were true because of pure coincidence.
"However, the mundane people not blessed by having the Inner Eye did not always like the fate that was awaiting them. As if boycotting my business would alter their fates." Sybill sniffed.
"Most interesting. And do tell me what kinds of divination you are planning to teach. Never having studied this subject, I am of course not an expert in this field but I think I will be able to follow you nonetheless." answered Albus Dumbledore.
Sybill seemed to pick up on his less than enthusiastic response and apparently tried to impress him by listing all ways to foretell fortunes he knew and then some more. In a way, it was impressive, he had to admit. There was no denying that Sybill Trelawney was very knowledgeable in her field, if he wanted to continue the subject, she would be the best teacher he would be able to hire seeing as how the real experts, the centaurs, would never agree to serve any human. But still, he felt it in his school's best interest to discontinue divination studies at Hogwarts.
He tried to prepare himself for the inevitable dreary reaction of the young woman and then started his hopefully polite refusal.
"While I do think you are an expert in your field" –her eyes shone at the unexpected praise- "I am afraid I will not be able to hire you. You see …" he tried to explain about his decision to discontinue teaching the obscure subject of Divination at Hogwarts when something altogether unexpected happened.
Sybill Trelawney's eyes rolled back in her head and in a hoarse voice that had nothing in common with its earlier breathiness declared apparently unconscious of his presence, "The one with the power to vanquish the Dark Lord approaches... Born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives..."
And while he was still hastening over to her to see if he could somehow assist her although she seemed perfectly alright there was a commotion at the door.
The Headmaster looked up in surprise to see the pub's owner angrily throwing out young Severus Snape who had apparently tried to listen in. This practically screamed danger, especially for the Seer who seemed quite bemused to finding him fussing over her. It was obvious she remembered nothing and Sybill even apologized for fainting, admitting somewhat ashamed that she hadn't eaten much that day. He made a quick decision.
"Your dedication and expertise in this branch of magic are certainly impressive. I am very pleased to tell you that I am looking forward to see you teaching at Hogwarts." he smiled. "When will you be able to start?"
His decision to hire her on the spot surprised Sybill Trelawney, after all she had thought he seemed not interested in her beloved subject. Better grab the opportunity as long as it's there, she thought.
"I am delighted, Professor. No indeed, I am most pleasantly surprised. Even though I foresaw that, of course." she hastily added. "I am available immediately"
Perfect, Albus Dumbledore thought, she obviously had no idea of the danger she had just placed herself him for Severus Snape was certain to rely the parts he had heard to his master.
"How about starting tomorrow, then? You could stay the night here and tomorrow you can move in and get started at Hogwarts. As long as the students are home for the summer break, you will be able to settle in, set the curriculum and make yourself familiar with the castle once more.", he suggested and upon agreement proceeded to clear most of the questions. He soon left Sybill who apparently still couldn't believe her good luck entirely. So much for predicting his answer.
On his way down he stopped to have a word with his brother about looking after his future divination teacher. Aberforth did agree to watch out for her, after voicing his opinion about hiring 'the most useless fraud we had to endure some quite some time'. "Oh, and just so you know, the bloke trying to listen in, the Snape boy, said something about confusing the door. Utter bullshit, that's what this is. And he said he was just trying to get some tips. Apparently wants to apply for a teaching post as well. Look out for that one." he grumbled.
Thanking him, the Headmaster made his way back to his castle. Things were as safe as he could make them without letting suspicions arise unnecessarily and tomorrow the Seer would be safe in Hogwarts where Tom would be unable to reach her. And the Hog's Head would have some extra protection tonight, in form of several Order members.
Albus Dumbledore hurried up to his office and extracted the fresh memory from his mind and let it fall into the pensieve. He bent over and allowed himself be sucked into his own memory.
Straightening up he hastily warned the two women to whom this prophecy could apply. Fortunately both Alice Longbottom and Lily Potter were members of the Order of the Phoenix and he was able to summon the pregnant women and their respective husbands to the Order's Headquarters and safety. Starting tomorrow they would work on safe houses for the two families.
Having done what was possible for the moment, he started to get to bed. He pondered the developments for some minutes before falling asleep. So true prophecies actually existed.
This morning he would never have guessed that he would actually witness his first true prophecy.