Harbouring Rancour

Resentment is linked with rancour. When the intellect forms the image of a brother's face with a feeling of resentment, it is clear that it harbours rancour against him. 'The way of the rancorous leads to death' (Prov. 12:28. LXX), because 'whoever harbours rancour is a transgressor' (Prov. 21:24. LXX).

If you harbour rancour against anybody, pray for him and you will prevent the passion from being aroused; for by means of prayer you will separate your resentment from the thought of the wrong he has done you. When you have become loving and compassionate towards him, you will wipe the passion completely from your soul. If somebody regards you with rancour, be pleasant to him, be humble and agreeable in his company, and you will deliver him from his passion.

St. Maximos the Confessor
Third Century on Love (from the Philokalia)

(Septuagint links here)