Tafsir of Yusuf 12:97

"They said, 'O our father, ask forgiveness for our sins for us.'" They requested from him—peace be upon him—the seeking of forgiveness, and addressed him with the title of fatherhood to stir his affection and compassion. They justified this by saying, "Indeed, we have been sinners."

That is, it is the right of one who confesses his sin that it be overlooked and that forgiveness be sought for him. It is as if they were confident in his pardon; thus, they limited themselves to requesting the seeking of forgiveness, and they incorporated that [confession] into the [request for] forgiveness.

It has also been said: When they addressed him as such, they meant, "It is the right of your compassion for us that you seek forgiveness for us, for were it not for that, we would be ruined for having committed the sin intentionally; so who would have mercy on us if you do not have mercy on us?" But this [interpretation] is not as sound.