It is narrated from Hazrat Nawas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "It is a great betrayal that you say something to your brother, he considers you truthful, while you are lying to him."
Hadith Referenceمسند احمد / مسند الشاميين / 17635
Hadith Gradingحکم دارالسلام:إسناده ضعيف جداً، من أجل عمر بن هارون، وقد تابعه عليه الوليد بن مسلم، لكن دلس فيه الوليد