Narrated Abu Hurairah:
that the Prophet (ﷺ) said: "Al-'Abbas is the uncle of the Messenger of Allah (ﷺ), and indeed, the uncle of a man is the Sinw of his father or from the Sinw of his father." (JA)
English reference (JA): Vol. 1, Book 46, Hadith 3761 (JA)
Arabic reference (JA): Book 49, Hadith 4128 (JA)