Musannaf Ibn Abi Shayba 24:146

Yahya ibn Ya'la narrated to us, from his father Ya'la ibn Harmala, who said: Al-Hajjaj spoke on the day of Arafah at Arafat and prolonged the speech. Abdullah ibn Umar said: "Beware, for today is a day of remembrance (dhikr)." But Al-Hajjaj continued. He said: Abdullah repeated it two or three times, then said: "O Nafi', call for the prayer." So Al-Hajjaj descended.