Musannaf Ibn Abi Shayba 3:5774

Ibn ‘Ulayyah narrated to us, from Ayyub, from Abu Qilabah, who said: A man who had read the letter of ‘Uthman—or to whom it was read—narrated to me, saying: "As for what follows: It has reached me that men among you go out to their lands, whether for loss, for tax collection, or for trade, and they shorten the prayer and do not complete the prayer. So do not do that. For indeed, only one who is traveling or in the presence of an enemy shortens the prayer."