Musnad Ahmad 2:29

Bahz narrated to us, Aban narrated to us, from Qatadah, from Abu al-Aliyah, from Ibn Abbas, who said: "Men who are pleasing to me bore witness before me, among them Umar, and the most pleasing of them to me is Umar: that the Prophet of Allah, may Allah bless him and grant him peace, used to say: 'There is no prayer after the Asr prayer until the sun sets, and there is no prayer after the Subh (Fajr) prayer until the sun rises.'"