It is narrated from Sayyiduna Sufyan bin Asid Hadhrami, may Allah be pleased with him, that he heard the Prophet, peace and blessings be upon him, say: "The greatest betrayal is that you speak to your brother about something, and he believes you to be truthful, while you are lying to him."
Hadith Referenceالادب المفرد / كتاب / 393
Hadith Gradingالألبانی:ضعيف
Hadith Takhrij«ضعيف : أخرجه المصنف فى التاريخ الكبير : 86/4 و أبوداؤد : 4973 و البيهقي فى الكبرىٰ : 199/10 - انظر الضعيفة : 1251»