What is the ruling regarding someone who imagined a woman during ablution, then uttered the phrase "This requires sincerity," and regretted it?

Wudu is not invalidated by obsessive thoughts (waswasa) about the intention to touch one's private parts (awra). The forbidden intention does not invalidate an act of worship unless it is acted upon, not merely by the intention itself. It is advised to turn away from these whispers and seek help from Allah and supplicate to get rid of them.