جامع الترمذي

Narrated Anas bin Malik: that the Prophet (ﷺ) said: "Whoever recited Qul Huwa Allahu Ahad two hundred times everyday, fifty years worth of his sins will be removed - unless he owed a debt." And another narration with this chain, from the Prophet (ﷺ) that he said: "Whoever wants to sleep upon his bed and sleeps on his right side, then he recites Qul Huwa Allahu Ahad one hundred times, then on the Day of Judgement the Lord, Blessed and Most High shall say: 'O My slave! Enter Paradise on your right.'"