Musnad Ahmad 32:1749

'Ali ibn Ishaq narrated to us, 'Abdullah informed us, al-Awza'i informed us, he said: Ishaq ibn 'Abdullah ibn Abi Talhah al-Ansari narrated to me, he said: Anas ibn Malik narrated to me, he said: "A year of drought afflicted the people during the time of the Messenger of Allah, may Allah bless him and grant him peace. He said: While the Messenger of Allah, may Allah bless him and grant him peace, was delivering the sermon on Friday, a Bedouin stood up and said: 'O Messenger of Allah, the wealth has perished and the family is hungry, so supplicate to Allah to give us rain.' The Messenger of Allah, may Allah bless him and grant him peace, raised his hands, and there was not a single patch of cloud in the sky. Then, clouds like mountains rose up, and he did not descend from his pulpit until we saw the rain cascading down his beard." He then mentioned the rest of the hadith.