“Bye, Al,” said Harry as his son hugged him. “Don’t forget Hagrid’s invited you to tea next Friday. Don’t mess with Peeves. Don’t duel anyone till you’ve learned how. And don’t let James wind you up.”
“What if I’m in Slytherin?”
The whisper was for his father alone, and Harry knew that only the moment of departure could have forced Albus to reveal how great and sincere that fear was.
Harry crouched down so that Albus’s face was slightly above his own. Alone of Harry’s three children, Albus had inherited Lily’s eyes.
“Albus Severus,” Harry said quietly, so that nobody but Ginny could hear, and she was tactful enough to pretend to be waving to Rose, who was now on the train, “you were named for two headmasters of Hogwarts. One of them was a Slytherin and he was probably the bravest mane I ever knew.”
“But just say –“
“– then Slytherin House will have gained an excellent student, won’t it? It doesn’t matter to us, Al. But if it matters to you, you’ll be able to choose Gryffindor over Slytherin. The Sorting Hat takes your choice into account.”
“It did for me,” said Harry.
He had never told any of his children that before, and he saw the wonder in Albus’s face when he said it.
Harry Potter and the Deathly Hallows – J.K. Rowling