Sahih Bukhari Volume 6, Book 60, Hadith Number 487.

Narrated By Abu Huraira : The Prophet was asked about donkeys and he replied, “Nothing has been revealed to me regarding donkeys except this comprehensive Verse which includes everything:

“So whoever does good equal to the weight of an atom (or a smallest ant) shall see it; And whoever, does evil equal to the weight of an atom or a smallest ant) shall see it.’ (99.7-8)