What is the legality of the Hajj performed by a Muslim, but was sponsored by a non-Muslim?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

There is no objection for the Muslim to accept gifts from non-Muslims, although he should not let this cause him to have affection towards this disbeliever or becoming his supporter and associate; Allaah Says (what means): {You will not find a people who believe in Allaah and the Last Day having affection for those who oppose Allaah and His Messenger, even if they were their fathers, or their sons, or their brothers, or their kindred…} [Quran 58:22]

So, if the Muslim gets some money from a disbeliever in a legal way (a gift, for instance), then this is considered lawful property. The Prophet, sallallaahu ‘alayhi wa sallam , accepted gifts from some polytheists such as gifts sent to him from the Caesar and Egypt's ruler at that time.

According to the opinion of the majority of the Muslim scholars if the money he gets is unlawful and he uses it to perform Hajj, his Hajj is valid but he has sinned, although Imaam Ahmad said, “The Hajj of the person who performs Hajj with ill-gotten money, is invalid.”

Allaah Knows best.