He nudged Buckbeak’s sides with his heels.
Buckbeak soared straight into the dark air. Harry gripped his flanks with his knees, feeling the great wings rising powerfully beneath him. Hermione was holding Harry very tight around the waist; he could hear her muttering, “Oh no- I don’t like this- oh, I really don’t like this-“
-page 413, Harry Potter and the Prisoner of Azkaban