Maliks Muwatta Book 21, Hadith Number 38.

Section : What is Disliked to be done with Something Given in the Way of Allah.

Yahya related to me from Malik from Yahya ibn Said that Umar ibn al-Khattab in one year gave 40,000 camels as mounts. Sometimes he would give one man a camel to himself. Sometimes he would give one camel between two men to take them to Iraq. A man from Iraq came to him and said, “Give Suhaym and I a mount. “Umar ibn al-Khattab said to him, “I demand from you, by Allah!, is Suhaym a water skin?” He said, “Yes.”