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].

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]‏ .‏