Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: When this verse was revealed: "Say: I do not ask you for any reward for this (conveying of the message) except love for near kin" [Surah al-Shura: 23], the Companions said: O Messenger of Allah, who are these near kin of yours whose love has become obligatory upon us? He (peace and blessings be upon him) said: "Ali, Fatimah and their two sons."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2628