Musannaf Ibn Abi Shayba 3:1139

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mis-haj bin Musa al-Dabbi, he said: I heard Anas bin Malik saying to Muhammad bin Amr: "When you are on a journey, and you say: 'Has the sun declined or has it not declined?' or 'Has the day reached its midpoint or has it not reached its midpoint?', then pray before you depart."