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.
Islam encourages good treatment and kindness to Muslims in general, and this is more confirmed to those who are related to the Muslim through a bond like the bond of marriage. This is supported by the saying of the Prophet, sallallaahu ‘alayhi wa sallam, which reads: "You will conquer Egypt where Qiraat (a coin or a unit of land measurement) is frequently mentioned. So, when you conquer it, be kind to its people because they have rights of protection and ties of kinship (upon you)." In another wording of the same Hadeeth, he said, “and rights because of the relationship of marriage.” [Muslim]
This indicates that kindness to in-laws is required, and this includes kindness in sayings, actions, and giving money in a manner that maintain amity and affection among people.
Such kindness is undoubtedly according to one's capacity. So, if your father-in-law became angry with you because you did not help him, he would be mistaken, particularly that you said that you were tied up. Therefore, we advise you first to be patient; then, to do your best to deal with the matter wisely and carefully. Seek the Help of Allaah The Almighty first, then the help of virtuous and notable people to achieve reconciliation between you; for {Reconciliation is best} as Allaah The Almighty said.
Allaah Knows best.