Nafi' bin Abd al-Harith said: Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) came to Makkah and entered Dar al-Nadwah on a Friday, wanting to set off from there to the Mosque, as it was close by. He threw his cloak over a peg in the house, and one of these pigeons landed on it. He shooed it away, and it landed (on another peg), and a snake seized it and killed it. When he had prayed the Friday prayer, Sayyiduna Uthman bin Affan (may Allah be pleased with him) and I went in to him, and he said: "Judge me concerning something I did today. I entered this house, wanting to set off from it to the Mosque since it is close, and I threw my cloak over this peg. One of these pigeons landed on it, and I feared it would soil it with its droppings, so I shooed it off. It landed on this other peg, and a snake seized it and killed it. I felt within myself that I had driven it from a place where it was safe to a spot where its death lay." So I said to Sayyiduna Uthman bin Affan (may Allah be pleased with him): "What do you think of a two-year-old, whitish she-goat, which we impose as a ruling on the Commander of the Believers?" He said: "I think so." So Umar (may Allah be pleased with him) ordered it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10002