Musnad Ahmad 1153:490

Uthman ibn Umar narrated to us, he said: Ubayd Allah ibn Hawdhah narrated to us, from Amr ibn Abd al-Rahman, from his paternal aunt, that she narrated to her from Aisha, who said: "I never saw any agitation on the face of the Messenger of Allah, may Allah bless him and grant him peace, until he saw a cloud. But when that cloud rained, that agitation would depart."