Musnad Ahmad 27:310

Waki' narrated to us, Shu'bah narrated to us, from Tawbah al-'Anbari, from Muwarriq al-'Ijli, who said: I said to Ibn 'Umar: "Do you pray the Duha (forenoon) prayer?" He said: "No." I said: "Did 'Umar pray it?" He said: "No." I said: "Did Abu Bakr pray it?" He said: "No." I said: "Did the Prophet, peace and blessings of Allah be upon him, pray it?" He said: "I do not think so."