Faith does not enter a man's heart until he loves you for the sake of Allah and His Messenger

It is narrated from al-Muttalib bin Rabi'ah that he said: Sayyiduna Abbas (may Allah be pleased with him) came to the Messenger of Allah (peace and blessings be upon him) in a state of anger. He (peace and blessings be upon him) asked: "What is the matter with you?" He said: O Messenger of Allah! What is the matter between us and Quraysh? He (peace and blessings be upon him) said: "What is the matter between you and them?" He said: When they meet one another, they meet with open and cheerful faces, but when they meet us, their manner is not like that (rather they show coldness). The narrator says: At this the Messenger of Allah (peace and blessings be upon him) became so angry that the vein between his two eyes swelled. Then when his anger subsided, he (peace and blessings be upon him) said: "By the One in whose hand is the soul of Muhammad (peace and blessings be upon him)! Faith cannot enter the heart of any man until he loves you for the sake of Allah and His Messenger." The narrator says: Then he (peace and blessings be upon him) said: "What is the matter with people who hurt me concerning Abbas? A man's uncle is just like his father."
This hadith was narrated by Isma'il bin Abi Khalid from Yazid bin Abi Ziyad. Although the two Shaykhs (Bukhari and Muslim) did not record the hadith of Yazid, he is one of the pillars of hadith (the major narrators) among the people of Kufah.

Sayyiduna Abdullah bin al-Harith narrates from Sayyiduna Abbas bin Abd al-Muttalib (may Allah be pleased with him) that he said: I said: O Messenger of Allah! Indeed, when Quraysh meet one another they meet with cheerful faces, and when they meet us they meet us with faces we do not recognise (that is, they turn their faces away). The narrator says: At this the Messenger of Allah (peace and blessings be upon him) became intensely angry and said: "By the One in whose hand is the soul of Muhammad (peace and blessings be upon him)! Faith cannot enter the heart of any man until he loves you for the sake of Allah and His Messenger."
I have mentioned part of this under the virtues of al-Hasan and al-Husayn (may Allah be pleased with them both) in "The Virtues of the Household of the Messenger of Allah (peace and blessings be upon him)", and by mentioning al-Muttalib bin Rabi'ah and those who dropped him from the chain, I have made clear the hidden defects ('ilal) of this hadith; so there is no need to repeat it in this place.

Makhul narrates from Sa'id bin al-Musayyab that he said: Sayyiduna Abbas bin Abd al-Muttalib (may Allah be pleased with him) is the best individual of this Ummah, the heir of the Prophet (peace and blessings be upon him) and his uncle.

Abu Salih Dhakwan relates from Suhayb, the freed slave of Sayyiduna Abbas (may Allah be pleased with him), that he said: Sayyiduna Abbas bin Abd al-Muttalib (may Allah be pleased with him) sent me to Sayyiduna Uthman (may Allah be pleased with him). I came to him and at that time he was feeding people the morning meal. I summoned him, and he came to him (Abbas, may Allah be pleased with him) and said: "O Abu al-Fadl! May your face be successful and prosperous." He replied: "And your face too, O Commander of the Faithful!" Sayyiduna Uthman (may Allah be pleased with him) said: "The only delay was that when your messenger came to me I was feeding people; I fed them and then came (straight to you)."

It is narrated from Amr bin Thabit that he said: A man came to Sayyiduna al-Husayn bin Ali (may Allah be pleased with them both) while he was eating, and he said: "Come near and eat." He said: I have already eaten. He asked: "With whom?" He said: With Ibn Abbas (may Allah be pleased with them both). He said: "Listen! Indeed, his father was the chief of Quraysh."

It is narrated from Sayyiduna Abdullah bin Tha'labah (may Allah be pleased with him) that he said: The Messenger of Allah (peace and blessings be upon him) said: "Allah Almighty has enjoined me to treat my relatives well, and has commanded me to begin (it) with Abbas (may Allah be pleased with him)."