Musnad Abu Ya'la al-Mawsili 110:226

Zuhayr narrated to us, Uthman ibn Umar narrated to us, Yunus narrated to us, from al-Zuhri, from Ubayd Allah ibn Abd Allah ibn Utbah, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) was the most generous of people, and he was at his most generous during Ramadan when Gabriel would meet him. He used to meet him every night in Ramadan to study the Quran with him. When Gabriel would meet him, the Messenger of Allah (may Allah bless him and grant him peace) was more generous than the sent wind.