Abu Dawud Book 36, Hadith Number 5080.
Chapter : Not known.
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.”