Is it valid to seek forgiveness for a sin not yet committed, out of fear of not having a later opportunity, or to seek general forgiveness for errors of the tongue before the end of the day?

Seeking forgiveness (Istighfar) is a great act of worship that brings much good in this world and the hereafter. Seeking forgiveness is for a sin that has passed, while for the future, there is repentance (Tawbah). Seeking forgiveness is also desirable after performing acts of obedience. Istighfar can be done at all times and in all circumstances, and it is not limited to a specific form. The Istighfar intended for repentance will only bear fruit if the conditions of repentance are met: abandoning the sin, regretting it, and resolving not to return to it. Whoever seeks forgiveness with his tongue while persisting in disobedience is like one who mocks his Lord.