What is the ruling on one who performed ablution for a long time without wiping the head, due to ignorance, and what is the ruling on his ablution and prayers during that period?

Ablution (wudu') is not valid without wiping over the head, as it is one of the agreed-upon obligatory acts of wudu'. Whoever does not wipe over their head has not completed their wudu' due to the omission of one of its pillars, and prayer performed with such wudu' is invalid. All prayers performed with this incomplete wudu' must be made up, whether the omission was due to ignorance or not. This is the view of the majority of scholars.

Shaykh al-Islam Ibn Taymiyyah is of the opinion that whoever omits wiping over the head due to ignorance of its ruling must repeat the prayer of that time and adhere to it in the future, but is not required to repeat past prayers. He bases this on the fact that the Prophet (peace be upon him) commanded the one who performed his prayer poorly to repeat the prayer of that time but did not command him to repeat past prayers.