Musnad Ahmad 1221:1

Sufyan narrated to us, Ubayd Allah ibn Abi Yazid narrated to us, from his father, from Siba’ ibn Thabit, who said: I heard from Umm Kurz al-Ka’biyyah, who narrates from the Prophet, may Allah bless him and grant him peace, she said: I heard the Prophet, may Allah bless him and grant him peace, at al-Hudaybiyyah, and I had gone to ask for some meat: "For the boy, two sheep, and for the girl, one sheep; it does not harm you whether they are male or female." She said: And I heard the Prophet, may Allah bless him and grant him peace, saying: "Leave the birds in their resting places."