Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1961
'Ata' b. Abi Rabah reported that he heard 'A'isha, the wife of the Apostle of Allah (way peace be upon him), as saying: When there was on any day windstorm or dark cloud (its effects) could be read on the face of the Messenger of Allah (may peace be upon him), and he moved forward and backward (in a state of anxiety) ; and when it rained, he was delighted and it (the state of restlessness) disappeared. 'A'isha said: I asked him the reason of this anxiety and he said: I was afraid that it might be a calamity that might fall upon my Ummah, and when he saw rainfall he said: It is the mercy (of Allah).