If a father obliges his son to marry the daughter of his brother and the son agreed as a sign of obedience to him but he was forced. Seven years after the engagement, the son refused to wrong his cousin by marrying her, so he told her the truth. So she supplicated against him. Will her supplication be accepted as he did not want to wrong her by marrying her?

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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

If a man refuses to marry his fiancée, this is not an injustice to her, especially if he fears that by marrying her, he would not fulfil her right. Therefore, it is not permissible for her to supplicate against him or against his relatives because of him refusing to go ahead with the marriage. Supplicating against any Muslim who has not wronged a person is a transgression in supplication, and this is forbidden. Ibn Taymiyyah said: 'It is forbidden to transgress in supplicating as Allaah Says (what means): {Indeed, Allaah does not like transgressors.}[Quran 2:190]. The transgression could be in the supplication itself by associating partners to Allaah or supplicating in an illegal way, or by supplicating something forbidden or supplicating against someone without due right.'

Even when a person is wronged, it is not permissible for him to supplicate with injustice or the cutting of relations with kinship, and he is not permitted to supplicate more than the wrong he was afflicted with, and it is more appropriate not to supplicate against him in principle, rather he should be patient and forgive him and put the matter in Allaah's Hands. Even when he wants to supplicate, he is permitted to only supplicate according to the wrong which was done to him; if he supplicates more than that, he is a transgressor.  

Allaah Knows best.