Musnad Ahmad 1789
Musnad Bani Hashim (Hadeeth of al-'Abbas bin 'Abdul-Muttalib from the Prophet)
It was narrated that "Ubaidullah bin "Abbas bin "Abdul-Muttalib, the brother of "Abdullah, said: Al-"Abbas had a downspout on the route taken by "Umar bin al-Khattab. One Friday, "Umar got dressed. Two chickens had been slaughtered for al-bas, and when ["Umar] passed by the downspout, water came out, mixed with blood of the two chickens. It landed on "Umar, and in it was the blood of the two chickens. "Umar ordered that the downspout be removed, then he went back and took off those clothes, and put on some other clothes. Then he came and led the people in prayer. Al-"Abbas came to him and said: By Allah, the downspout is where the Prophet (ﷺ) put it. So ʻUmar said to al-"Abbas: I insist that you should climb onto my back and put it where the Messenger of Allah (ﷺ) put it. So al-"Abbas (رضي الله عنه) did that.