Musnad Ahmad 21:27

Asbat ibn Muhammad narrated to us, Hisham ibn Sa’d narrated to us, from Ubayd Allah ibn Abbas ibn Abd al-Muttalib, the brother of Abdullah, who said: Al-Abbas had a water spout over the path of Umar ibn al-Khattab. Umar put on his clothes on a Friday, and two chicks had been slaughtered for al-Abbas. When he reached the water spout, it poured water containing the blood of the two chicks, and it struck Umar while it contained the blood of the chicks. Umar ordered it to be removed. Then Umar returned, took off his clothes, and put on clothes other than his clothes. Then he came and prayed with the people. Al-Abbas came to him and said, "By Allah, it is the place where the Prophet, peace and blessings of Allah be upon him, placed it." Umar said to al-Abbas, "And I adjure you to climb upon my back until you place it in the place where the Messenger of Allah, peace and blessings of Allah be upon him, placed it." So al-Abbas, may Allah be pleased with him, did that.