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." (ID)
English reference (ID): Vol. 5, Book 42, Hadith 2898 (ID)
Arabic reference (ID): Book 45, Hadith 3143 (ID)