Musannaf Ibn Abi Shayba 3:5824

Waki’ narrated to us, he said: Shu’bah narrated to us, from Abu al-Tayyah al-Dab’i, from a man from ‘Anazah whose kunya was Abu al-Minhal, he said: I said to Ibn Abbas: "I stay in Medina for a year, and I do not tighten the straps (for travel)." He said: "Pray two rak'ahs."