Sahih Bukhari Volume 1, Book 2, Hadith Number 40

Narated By Abu Huraira : Allah’s Apostle said, “If any one of you improve (follows strictly) his Islamic religion then his good deeds will be rewarded ten times to seven hundred times for each good deed and a bad deed will be recorded as it is.”

References

Reference: Sahih al-Bukhari 42
In-Book Reference: Sahih al-Bukhari Book 2 Hadith 35