Sirius and Buckbeak went into hiding again that day and moved around often, so they wouldn’t be caught. A day before he knew the last day of school was, Sirius wrote a letter to Harry, which read

Dear Harry,

I hope this finds you before you reach your aunt and uncle. I don't know whether they're used to owl post.

Buckbeak and I are in hiding. I won't tell you where, in case this owl falls into the wrong hands. I have some doubt about his reliability, but he is the best I could find, and he did seem eager for the job.

I believe the Dementors are still searching for me, but they haven't a hope of finding me here. I am planning to allow some Muggles to glimpse me soon, a long way from Hogwarts, so that the security on the castle will be lifted.

There is something I never got around to telling you during our brief meeting. It was I who sent you the Firebolt.

Crookshanks took the order to the Owl Office for me. I used your name but told them to take the gold from my own Gringotts vault. Please consider it as thirteen birthdays' worth of presents from your godfather.

I would also like to apologize for the fright I think I gave you that night last year when you left your uncle's house. I had only hoped to get a glimpse of you before starting my journey north, but I think the sight of me alarmed you.

I am enclosing something else for you, which I think will make your next year at Hogwarts more enjoyable.

If ever you need me, send word. Your owl will find me.

I'll write again soon.

Sirius

The thing he had enclosed was this,

I, Sirius Black, Harry Potter's godfather, hereby give him permission to visit Hogsmeade on weekends. There was also a P.S,

I thought your friend Ron might like to keep this owl, as it's my fault he no longer has a rat.