Five ways to overcome arisen resentment - 1) loving-kindness, 2) compassion, 3) equanimity, 4) disregarding and non-attention, 5) reflection on kamma.
Paṭhamaāghātapaṭivinaya sutta - Overcoming Resentment (First)
The First Discourse on overcoming Resentment
Bhikkhus, there are these five ways to overcome resentment by means of which resentment that has arisen in a bhikkhu is completely overcome. What five?
Bhikkhus, in whoever resentment might arise, loving-kindness should be cultivated towards that person. Thus, the resentment towards that person should be overcome.
Bhikkhus, in whoever resentment might arise, compassion should be cultivated towards that person. Thus, the resentment towards that person should be overcome.
Bhikkhus, in whoever resentment might arise, equanimity should be cultivated towards that person. Thus, the resentment towards that person should be overcome.
Bhikkhus, in whoever resentment might arise, disregarding and non-attention should be applied towards that person. Thus, the resentment towards that person should be overcome.
Bhikkhus, in whoever resentment might arise, reflection on kamma should be determined towards that person: 'He is the owner of his actions, heir to his actions, born of his actions, related to his actions, supported by his actions. Whatever actions he does, whether good or bad, he will be the heir of those.' Thus, the resentment towards that person should be overcome.
Bhikkhus, these are the five ways to overcome resentment by means of which resentment that has arisen in a bhikkhu is completely overcome.