one night after the entire common room was asleep. Harry went down into the library restricted section to look up Nicholas Flamel. While looking at books, Harry gets startled by Mrs Norris and sneaks out of the library.

While running through the corridor. Harry sees Severus talking to Quirrell while throwing him against the wall.

"Now I'm going to say this once and only once Quirrell, Stay away from the boy or else." Severus sneered.

"Ww-whhy-Why shhhh should i severus?" Quirrell asked.

"Because i said so. And don't even think about going through those traps, i know it was you trying to get passed the Cerberus." Severus sneered.

"Ffffine, i'll have to be more careful." Quirrell said.