Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates this as a marfu' hadith: The Prophet (peace and blessings be upon him) said: "When a man honours his brother, he is honouring his Lord."
Al-Bazzar recorded it. Its chain contains al-Hajjaj bin Artah and Mus'ab bin Salam, both of whom are da'if (weak), though they have been declared trustworthy. The remaining narrators of this report are the narrators of the Sahih. Reports concerning the rights of a Muslim and showing mercy to people will come later in the chapter on righteousness and maintaining ties of kinship.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 12628