Musannaf Ibn Abi Shayba 24:109

Waki’ narrated to us, from Shu’bah, from Yahya ibn al-Husayn, from Tariq ibn Shihab, who said: There was a verbal dispute between Khalid ibn al-Walid and Sa’d. A man then spoke ill of Khalid in the presence of Sa’d. Sa’d said: "What is between us has not reached [the level of] our religion."