The Messenger of Allah ﷺ said, "Whoever says 'Glory be to Allah and praise be to Him' one hundred times will have his sins forgiven, even if they were like the foam of the sea."
حدثنا نصر بن عبد الرحمن الوشاء حدثنا عبد الرحمن المحاربي عن مالك بن أنس عن سمي عن أبي صالح
قال رسول الله ﷺ من قال سبحان الله وبحمده مائة مرة غفرت له ذنوبه ولو كانت مثل زبد البحر
Sourcing, [sahih] Tirmidhi narrated it in the Book of Supplications, chapter on the virtues of "Glory be to Allah and praise be to Him"... hadith 3466, from Nasr bin Abdul-Rahman, with this wording, and he said, hasan sahih. He also narrated it, hadith 3468, from the hadith of Maen, from Malik, with this wording, and he said, hasan sahih.