Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) was asked: Tell us about the time of hardship. Sayyiduna Umar (may Allah be pleased with him) said: We set out for the expedition of Tabuk on an intensely hot day. We camped at a place, and because of severe thirst our necks were close to breaking. A man would go out in search of water but would fear that his neck would break before he returned, until people would slaughter a camel, squeeze the water out of its stomach contents and drink it. Then Sayyiduna Abu Bakr (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) to supplicate for good. He (peace and blessings be upon him) said: "Would you like that?" Sayyiduna Abu Bakr (may Allah be pleased with him) answered yes. Then the Prophet (peace and blessings be upon him) raised his hands and it rained, and the people filled their vessels with water. Then we went to look, and found that the rain had not gone beyond the army.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19641