What is the sin that is forgiven by fasting Ramadan out of faith and hope for reward—is it past sins or future sins?

"What has preceded of sin" refers to past sins. It has been reported in the Hadith that "whoever fasts Ramadan out of faith and hope for reward, his past sins will be forgiven," and this is interpreted as referring to minor sins. There is another narration with the addition of "and what will follow," meaning the forgiveness of future sins as well. Scholars have interpreted this to mean either protection from falling into major sins thereafter, or that any sins committed will be forgiven. Atonement expiates minor sins, alleviates major sins, and raises one's ranks in Paradise.