Jarir bin Abdullah (may Allah be pleased with him) says: "I pledged allegiance to the Prophet (ﷺ) to be sincere to every Muslim."
Hadith Referenceمسند الإمام الشافعي / كتاب فضائل قريش وغيرهم وأبواب متفرقة / 1804
Hadith Takhrijاخرجه البخاري، الایمان، باب قول النبي صلی اللہ علیہ وسلم الدين النصيحة .... الخ (57) ، (58) ومسلم، الايمان، باب بيان أن الدين النصيحة (56)۔
Tamim Dari (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: "Religion is the name of sincerity." Religion is the name of being sincere: to Allah, to His Prophet (peace and blessings be upon him), to the leaders of the Muslims, and to the common Muslims."
Hadith Referenceمسند الإمام الشافعي / كتاب فضائل قريش وغيرهم وأبواب متفرقة / 1805
Hadith Takhrijاخرجه مسلم الايمان، باب بيان أن الدين النصيحة (55)۔
It is narrated from Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "May Allah keep fresh the face of that servant who heard my words, preserved them, remembered them, and conveyed them to others. For sometimes the bearer of knowledge is not himself a jurist (i.e., does not possess the ability of deduction), and sometimes the bearer of knowledge conveys it to one who is more of a jurist than himself. There are three qualities in which the heart of a Muslim does not betray (i.e., a Muslim adopts them wholeheartedly): acting sincerely for the sake of Allah, wishing well for the Muslims, and remaining attached to the community of Muslims, for their supplication encompasses them from behind."
Hadith Referenceمسند الإمام الشافعي / كتاب فضائل قريش وغيرهم وأبواب متفرقة / 1806
Hadith Takhrijاخرجه الترمذى، العلم، باب ما جاء في الحث على تبليغ السماع (2657)، (2658) وقال حسن صحیح وابن ماجة ، السنة، باب من بلغ علماء (232) وصححه ابن حبان۔