Sayyiduna Jarir (may Allah be pleased with him) said: I came to the Prophet (peace and blessings be upon him) to pledge allegiance to him on Islam, and he (peace and blessings be upon him) held back his hand (and said): "And on sincere goodwill towards every Muslim (pledge allegiance as well)."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2471