ENOfficial
Abu Umama told of Abu Dharr asking God’s Prophet to tell him what the reward for sadaqa would be, and receiving the reply, “Many times as much, and more still with God.” Ahmad transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَبِي أُمَامَةَ قَالَ: قَالَ أَبُو ذَرٍّ: يَا نَبِيَّ اللَّهِ أَرَأَيْتَ الصَّدَقَةُ مَاذَا هِيَ؟ قَالَ: «أَضْعَافٌ مُضَاعَفَةٌ وَعِنْدَ اللَّهِ الْمَزِيدُ» . رَوَاهُ أَحْمد
sunnah.com