Sayyiduna Abd al-Rahman bin Uthman (may Allah be pleased with him) said: I said: "Tonight I will certainly stand at the Station of Ibrahim", so I arrived there before everyone else. While I was praying, a man placed his hand on my back. I looked, and it was Sayyiduna Uthman bin Affan (may Allah be pleased with him), who was the Commander of the Believers in those days. I moved back. He stood and recited the entire Qur'an, then bowed and sat, then recited the tashahhud and said the salam after one rak'ah, adding nothing to it. When he finished, I asked: "O Commander of the Believers! One rak'ah?" He said: "This is my witr."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4783