Sayyiduna Yusuf bin Abdullah bin Salam (may Allah be pleased with him) reports that the Prophet (peace and blessings be upon him) said: "The greatest form of zina (adultery) is that one of you assails the honour of his Muslim brother."
This narration was recorded by Imam al-Tabarani in al-Mu'jam al-Awsat from his teacher Muhammad bin Musa al-Ayli, from Amr bin Yahya al-Ubulli, and I do not know either of them; the remaining narrators of this narration are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 13134
Hadith Gradingمحدثین:إسنادہ ضعیف
Hadith Takhrij«اخرجه الطبراني فى المعجم الصغير (862) ، أخرجه المعجم الأوسط للطبراني برقم: 6127»