When wiping my head during Wudu', I fill my hands with new water and wipe from the front to the back, but the hair at the back remains dry because the water concentrates at the front. My hair is a little long, and I cannot wipe back and forth. Is my Wudu' valid?

All praise is due to Allah. Wiping the head is one of the pillars of ablution (wudu'), without which it is invalid. Scholars differed regarding the sufficient amount to wipe. According to the view that requires wiping the entire head, it is obligatory to repeat the wiping if one is certain that water did not reach a part of the hair. However, it is generally understood that wiping does not require water to reach every part of the hair, unlike washing. As for the view of those who do not obligate comprehensive wiping, then there is nothing for you to do. The person afflicted with obsessive doubts (waswasah) should adopt the easiest of opinions until Allah grants them recovery. It is recommended to consistently make supplication (du'a), show humility, and consult a trusted psychiatrist when experiencing obsessive doubts.