Musnad Ahmad 1153:1064

Waki’ narrated to us, from Sharik, from al-‘Abbas ibn Dharih, from al-Bahiy, from ‘Aishah, that Usamah stumbled at the threshold of the door, and he bled. He said: So the Prophet, may Allah bless him and grant him peace, began to suck it and say: "If Usamah were a girl, I would have adorned her and clothed her until I married her off."