Abu Dawud
General Behavior
Book Number: 036 / Hadith Number: 5080
Narated By 'Aisha, Ummul Mu'minin : When the Prophet (pbuh) saw a cloud formation in the sky, he left work, even if he were at prayer, and then would say: "O Allah! I seek refuge in Thee from its evil. " If it rained, he would say: "O Allah! send a beneficial downpour."