Sahih Bukhari, Chapter: Pilgrimage (Hajj)

Ubaidullah was asked about Al Mahassab. Ubaidullah narrated: Nafi said, 'Allah's Apostles, 'Umar and Ibn 'Umar camped there." Nafi added, "Ibn Umar used to offer the Zuhr and Asr prayers at it (i.e. Al-Mahassab)." I think he mentioned the Maghrib prayer also. I said, "I don't doubt about 'Isha' (i.e. he used to offer it there also), and he used to sleep there for a while. He used to say, 'The Prophet used to do the same.' "