Musnad Ahmad 788:187

Abu Dawud al-Hafari narrated to us, Sufyan narrated to us, from Qays ibn Muslim, from Tariq ibn Shihab, who said: Abu Musa said: I arrived from Yemen. He said: The Prophet, peace and blessings of Allah be upon him, said to me: "With what did you enter into Ihram?" He said: I said: With an Ihram like the Ihram of the Prophet, peace and blessings of Allah be upon him. He said: He said: "Do you have any sacrificial animal with you?" He said: I said: Meaning no. He said: So he commanded me, and I performed Tawaf around the House, and between al-Safa and al-Marwah, then I went to a woman from my people, and she combed my hair and washed it, then I exited Ihram. Then, when it was the Day of Tarwiyah, I entered into Ihram for Hajj. He said: I used to issue fatwas to the people regarding that during the leadership of Abu Bakr and Umar. While I was standing in the market of the season, a man came and whispered to me, saying: You do not know what the Commander of the Faithful has introduced regarding the matter of the rituals. He said: I said: O people, whoever we have issued a fatwa to regarding something, let him wait, for this is the Commander of the Faithful coming to you, so follow him. He said: He said to me: If we take the Book of Allah the Exalted, it commands completion, and if we take the Sunnah of our Prophet, peace and blessings of Allah be upon him, he "did not exit Ihram until he slaughtered the sacrificial animal."