All things are three at Hogwarts

Chapter 491 Selection (modified, sincere thanks to alliance leader You Mingzhi Yu)

Unlike Alan, who was popular among freshmen, the Gryffindor common room was a different scene at this time.

Seeing the new students and even Ron following Hermione timidly, Harry was sure that he certainly did not look so immature when he first came to Hogwarts. ...