Ata' bin Abi Rabah narrates that he heard Sayyidah Aishah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), saying: On a day when the wind blew or the clouds gathered, the anxiety and worry because of it would be apparent on his (peace and blessings be upon him) blessed face, and because of this he (peace and blessings be upon him) would at times come (into the room) and at times go (out). When the rain fell, he (peace and blessings be upon him) would become happy and his (peace and blessings be upon him) state of worry would end. Sayyidah Aishah (may Allah be pleased with her) said: I asked him (peace and blessings be upon him) about this, and he (peace and blessings be upon him) said: "I fear that it might be a punishment unleashed upon my Ummah." And when he saw the rain, he (peace and blessings be upon him) would say: "(It is) mercy, (it is) mercy." In a narration of Mu'adh the words are: "That state would be lifted from him (peace and blessings be upon him) and that (worry) would leave him (peace and blessings be upon him)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6465