What should I do about a wandering mind and thinking about worldly matters during prayer? Is it valid to repeat the prayer because of this, or is seeking forgiveness and resolving to be more devout in the next obligatory prayer sufficient?

Intrusive thoughts and self-talk during prayer do not invalidate it, even if prolonged. While devotion and full concentration are recommended during prayer, a lack thereof does not invalidate it. Scholars have adduced as proof for this the hadith of Abu Hurayrah: "Indeed, Allah has forgiven my Ummah for whatever occurs to them in their thoughts, as long as they do not act upon it or speak of it."

One who experiences such thoughts is not commanded to repeat the prayer, and a prayer is not to be repeated if it has fulfilled its conditions and pillars. However, the worshipper should strive to achieve devotion in prayer and compensate for any shortcomings by performing abundant supererogatory prayers.