بُلُوغُ الْمَرَامِ
Bulugh al-Maram 842
Business Transactions
وَعَنْ أَبِي أُمَامَةَ - رضى الله عنه - عَنِ اَلنَّبِيِّ - صلى الله عليه وسلم -قَالَ: { مَنْ شَفَعَ لِأَخِيهِ شَفَاعَةً, فَأَهْدَى لَهُ هَدِيَّةً, فَقَبِلَهَا, فَقَدْ أَتَى بَابًا عَظِيماً مِنْ أَبْوَابِ اَلرِّبَا } رَوَاهُ أَحْمَدُ, وَأَبُو دَاوُدَ, وَفِي إِسْنَادِهِ مَقَالٌ [1] .
Narrated Abu Umamah (RA): The Prophet (ﷺ) said: "Whoever intercedes for his brother and that one gives him a gift for that (intercession) which he accepts, he has engaged in one of the most terrible types of Riba (undeserving increase in something)." [Reported by Ahmad and Abu Dawud, but one of its narrators' reliability has been doubted].
Sunnah.com reference: Book 7, Hadith 77