Musnad Ahmad 2:37

Abu al-Mughirah narrated to us, al-Awza'i narrated to us, 'Amr ibn Shu'ayb narrated to us, from 'Abdullah ibn 'Amr ibn al-'As, from 'Umar ibn al-Khattab, that the Messenger of Allah (may Allah bless him and grant him peace) said: "There is no prayer after the morning prayer until the sun rises, and [there is no prayer] after the afternoon prayer until the sun sets."