What should I do about swearing an oath to pay the taxi fare, then my neighbor paid it; do I pay expiation for the oath or reimburse the neighbor for the fare amount?

Whoever swears an oath concerning a future action and then fails to do it, must offer an expiation for breaking an oath (kaffarat yamin (definition)). This is what the Permanent Committee for Scholarly Research and Ifta’ has ruled, and what Ibn Uthaymeen affirmed, clarifying that the expiation is: feeding ten needy persons, or clothing them, or emancipating a slave. If one cannot find any of these, then one must fast for three days, in accordance with the verse: ﴿Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families, or clothing them, or freeing a slave. But whoever finds not [the means], then a fast of three days. That is the expiation for your oaths when you have sworn.﴾ He advised against swearing oaths unless accompanied by the phrase "in shaa Allah" (if Allah wills) to avoid expiation if one fails to fulfill the oath.