Musnad Ahmad 482:86

Waki’ narrated to us, from Musa ibn ‘Ali, from his father, who said: I heard ‘Uqbah ibn ‘Amir al-Juhani saying: "There are three times during which the Messenger of Allah (may Allah bless him and grant him peace) used to forbid us from praying or from burying our dead: when the sun rises clearly until it ascends, when the sun is at its zenith until it declines, and when it leans toward setting until it sets."