Narrated Abu Sa'id Al Khudri:

Allah's Messenger (ﷺ) said, "If a person embraces Islam sincerely, then Allah shall forgive all his past sins, and after that starts the settlement of accounts, the reward of his good deeds will be ten times to seven hundred times for each good deed and one evil deed will be recorded as it is unless Allah forgives it."

Reference : Sahih-Bukhari 41
In Book Reference : Book 2, Hadith 34