سنن أبي داود

Narrated Aisha, Ummul Mu'minin (mother of the believers):

When the Prophet (ﷺ) saw a cloud formation in the sky, he would stop what he was doing, even if he were in prayer, and then would say: "O Allah! I seek refuge in You from its evil. "If it rained, he would say: "O Allah! send a beneficial downpour."