I heard the Messenger of Allah ﷺ say: It is great treachery that you should tell your brother something and have him believe you when you are lying.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ كَبُرَتْ خِيَانَةً أَنْ تُحَدِّثَ أَخَاكَ حَدِيثًا هُوَ لَكَ بِهِ مُصَدِّقٌ وَأَنْتَ لَهُ بِهِ كَاذِبٌ