Majma al-Zawaid — Hadith 10327

Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: It was said to Sayyiduna Umar bin al-Khattab (may Allah be pleased with him): "Tell us about the Battle of Tabuk." So Sayyiduna Umar (may Allah be pleased with him) said: We set out with the Prophet (peace and blessings be upon him) towards Tabuk; it was a season of intense heat. We camped at a place where severe thirst had overtaken us, so much so that we felt as though our necks would be severed, so much so that when one of us would go to relieve himself, before he returned he would feel that his neck would be severed, and so much so that when a man slaughtered his camel, he would squeeze out its dung and drink it and place it on his stomach.
Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) said: "O Messenger of Allah, Allah Almighty has placed blessing in your supplication, so supplicate to Allah Almighty." The Prophet (peace and blessings be upon him) asked: "O Abu Bakr, would you like that?" He said: "Yes." So the Prophet (peace and blessings be upon him) raised both his hands, and his hands had not yet come down when rain began to fall from the sky, and so much rain fell that the people filled all the things they had with them. Then we looked around and found out that it had not rained anywhere except in the area of the army.
Al-Bazzar recorded it, and al-Tabarani recorded it in al-Mu'jam al-Awsat. The narrators of al-Bazzar are thiqat (trustworthy).