What is the ruling on the Hajj if the pilgrim discovers afterwards that he used to wash his hands after his head, ears, and neck when performing ablution (wudu'), and that all his prayers and Hajj rituals were performed with this ablution which he believed to be valid?

A Muslim is legally obligated to learn the rulings of his acts of worship, including ablution (wudu'). The legitimacy of ablution includes wiping over the head, and the majority of scholars do not consider wiping or washing the neck to be required. The order among the ablution limbs is obligatory according to the Shafi'is and Hanbalis, while it is a Sunnah (definition) according to the Hanafis and Malikis. Therefore, the questioner must observe the order in the future. As for what has passed, there is no need to repeat prayers or circumambulations (tawaf (definition)) based on the opinion of those who consider the order to be a Sunnah.