Abu Hurairah reported,

The Messenger of Allah ﷺ said, "Allah says, 'Every deed of the son of Adam belongs to him, except fasting. It is Mine, and I Myself reward it. He gives up his food and his drink for My sake, so his fasting is for Me, and I Myself reward it. Every good deed is repaid tenfold, up to seven hundred times over, except fasting. It is Mine, and I Myself reward it.'"

وقال قال رسول الله ﷺ يقول الله عز وجل كل عمل ابن آدم له إلا الصيام فهو لي وأنا أجزي به إنما يترك طعامه وشرابه من أجلي فصيامه له وأنا أجزي به كل حسنة بعشر أمثالها إلى سبع مائة ضعف إلا الصيام فهو لي وأنا أجزي به