Sufyan ibn Usayd al-Hadrami reported that he heard the Prophet ﷺ say, "It is great treachery to tell something to your brother so that he believes you when you are lying to him."

حَدَّثَهُ أَنَّهُ سَمِعَ النَّبِيَّ ﷺ يَقُولُ كَبُرَتْ خِيَانَةً أَنْ تُحَدِّثَ أَخَاكَ حَدِيثًا هُوَ لَكَ مُصَدِّقٌ وَأَنْتَ لَهُ كَاذِبٌ