Musnad Ahmad 409:1

Abdullah ibn Ahmad said: Abu Musa al-Anazi narrated to me, he said: Abd al-Samad ibn Abd al-Warith narrated to us, he said: Sakan ibn al-Mughirah narrated to me, he said: al-Walid ibn Abi Hisham narrated to me, from Farqad Abu Talhah, from Abd al-Rahman ibn Khabbab al-Sulami, who said: The Messenger of Allah (peace and blessings of Allah be upon him) delivered a sermon and encouraged [the people to support] the Army of Hardship. Uthman ibn Affan said: "I will provide one hundred camels with their saddlecloths and saddles." He said: "Then he encouraged [them again]." Uthman said: "I will provide another hundred with their saddlecloths and saddles." He said: "Then he descended one step from the pulpit and encouraged [them again]." Uthman ibn Affan said: "I will provide another hundred with their saddlecloths and saddles." He said: I saw the Prophet (peace and blessings of Allah be upon him) saying with his hand like this, moving it—and Abd al-Samad extended his hand as one who is astonished—"Nothing will harm Uthman for what he does after this."