I have reconciled two persons and one of them said that he had taken an oath so I told him that I would offer the expiation on his behalf even though he is well off. Is this permissible?

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.

Making settlement between adversaries is one of the most glorious acts of worship. Allaah The Almighty Says (what means): {so make settlement between your brothers.} [Quran 49:10]

It is narrated on the authority of Abu Ad-Dardaa’ that the Prophet, sallallaahu ‘alayhi wa sallam, said, "Shall I not inform you of something more excellent in degree than (supererogatory) fasting, prayer and almsgiving?” The people replied, “Yes.” The Prophet, sallallaahu ‘alayhi wa sallam, said, “It is reconciling people, because spoiling relationships between them is the shaver (of faith)." [Ahmad, Abu Daawood and At-Tirmithi who rendered it Hasan Saheeh]

Your commitment to make the oath expiation that is due on one of them to help him accept reconciliation with the other makes it obligatory on you. If you make it on his behalf, he will be free of liability.

Allaah Knows best.