Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said, “When one of you perfects his Islam, then every good deed he does is written as ten good deeds up to seven hundred times as much, and every bad deed he does is written as one bad deed.”

Source: Sahih Bukhari 42, Sahih Muslim 129

Grade: Muttafaqun Alayhi (authenticity agreed upon) according to Al-Bukhari and Muslim

For ARABIC, click here:

http://dailyhadith.abuaminaelias.com/2012/05/21/hadith-on-islam-the-muslims-who-perfects-his-islam-will-have-his-good-deeds-multiplied/