What should a pilgrim do if he passes wind while heading to circumambulate the Kaaba or to Arafat?

First: The majority of scholars hold the view that circumambulation (Tawaf (definition)) is not valid without purity. Therefore, if a person's ablution (wudu) breaks while they are proceeding to perform Tawaf, they should go and perform ablution, and then commence their Tawaf.

Second: As for the standing at Arafat, purity is not a prerequisite for it. Thus, it is valid for a pilgrim to stand at Arafat while not in a state of ablution, and ablution is not required of them except when they intend to pray. Scholars have reached a consensus on the validity of the standing of a menstruating woman and someone in a state of major ritual impurity (junub). However, it is recommended to stand in a state of purity from both minor and major impurities, because one will be engaging in remembrance of Allah the Almighty.