Musannaf Ibn Abi Shayba 17:1217

Waki’ narrated to us, from Usama bin Zayd, from Talha bin Ubayd Allah bin Kurayz, who said: Umar said: "If one of you knew what he has in saying to his brother, 'May Allah reward you with good' (Jazak Allahu Khayran), you would increase in saying it to one another."