Mishkat al-Masabih #1440

‘A’isha said that when the Prophet saw something rising in the sky, meaning clouds, he left what he was doing, faced them and said, "O God, I seek refuge in Thee from the evil of what they contain." If God cleared them away he praised Him, and if rain fell he said, "O God, give a beneficial fall.” Abu Dawud, Nasa’i, Ibn Majah and Shafi'i transmitted it, the wording being Shafi'i's.