Musnad Ahmad 27:213

Yahya narrated to us, from Ubaydullah, Nafi’ informed me, from Ibn Umar, who said: "I prayed with the Messenger of Allah, peace and blessings of Allah be upon him, two prostrations before Dhuhr, and two prostrations after it, and two prostrations after Maghrib, and two prostrations after Isha, and two prostrations after Jumu'ah. As for Jumu'ah and Maghrib, they were in his house." He said: "And my sister Hafsa informed me that he used to pray two light prostrations when the dawn broke." He said: "And it was a time when I would not enter upon the Prophet, peace and blessings of Allah be upon him."