Khaythama reported,
Saad bin Abu Waqqas was sitting with a group of people when they began mentioning Ali and insulting him.Saad said, "Hold back from speaking ill of the companions of the Messenger of Allah ﷺ. We acquired worldly gains alongside the Messenger of Allah ﷺ, and Allah 
revealed, "Had it not been for a prior decree from Allah, a severe punishment would have touched you for what you took" [Anfal 8:68]. So I hope that this was a mercy from Allah that preceded for us."One of them said, "By Allah, so-and-so used to hate you and insult you."Saad laughed until laughter overtook him, then said, "Does a man not sometimes hold a grievance against his brother over something between the two of them, yet it does not reach the point of betraying his trust?" And he mentioned another statement.
Azami 12417
Sahihعن خيثمة قال
كان سعد بن أبي وقاص في نفر، فذكروا عليا، فشتموه، فقال سعد: مهلا عن أصحاب رسول الله ﷺ، فإنا أصبنا دنيا مع رسول الله ﷺ، فأنزل الله عز وجل: {لولا كتب من الله سبق لمسكم فيما أخذتم عذاب عظيم}، فأرجو أن تكون رحمة من عند الله سبقت لنا، فقال بعضهم: فو الله إن كان ليبغضك، ويشتمك الأخينس، فضحك سعد حتى استعلاه الضحك. ثم قال: أوليس الرجل قد يجد على أخيه في الأمر يكون بينه و بينه، ثم لا يبلغ ذلك أمانته، وذكر كلمة أخرى.
No references are available.
Ibn Abu Hatim narrated it in his Tafsir (5/1734), and Hakim (2/329-330) - and this is his wording - both of them through the route of Ubaydullah bin Amr Raqqi, from Zayd bin Abu Unaysa, from Amr bin Mura, from Khaythama, who said, then he related it.Hakim said, "This is a sahih hadith according to the criteria of the two Shaykhs (Bukhari and Muslim), though they did not include it."