The Messenger of Allah ﷺ said, "Whoever says 'Glory be to Allah and praise be to Him' a hundred times in a day will have his sins wiped away, even if they were like the foam of the sea."
قال قرأت على عبد الرحمن: مالك عن سمي مولى أبي بكر عن أبي صالح السمان
أن رسول الله ﷺ قال من قال سبحان الله وبحمده في يوم مائة مرة حطت خطاياه وإن كانت مثل زبد البحر
Its isnad is sahih. It is in Muwatta, pages 209-210, and Bukhari related it, 11:173, via Malik. Muslim related it, 2:310, with similar meaning and different wording, via Suhayl from Sumayy. Tirmidhi and Ibn Majah also related it, as mentioned in Fath Kabir, 3:219.