Sunan At-Tirmidhi

Narrated Khuraim bin Fatik: That the Messenger of Allah (ﷺ) said: ""Whoever spends a sum in the cause of Allah, it is recorded for him seven-hundred fold."" [Abu 'Eisa said:] There are something on this topic from Abu Hurairah. This Hadith is Hasan, we only know of it from the narration of Ar-Rukain bin Ar-Rabi' (a narrator in the chain of this Hadith)