Musnad Ahmad 936:6

Hushaym narrated to us, Yunus informed us, from al-Hasan, that Umar wanted to forbid the Mut'ah of Hajj. My father said to him: "That is not for you; we performed Mut'ah with the Messenger of Allah, may Allah bless him and grant him peace, and he did not forbid us from that." So Umar refrained from that. And he wanted to forbid the *Hullah* (garments) of *Hibarah* because they were dyed with urine. My father said to him: "That is not for you; the Prophet, may Allah bless him and grant him peace, wore them, and we wore them during his era."