Is a questioner obligated to fulfill a vow to slaughter an animal as expiation for a forbidden act from which he repented, after he had vowed that due to his ignorance of the Sharia rulings, knowing that he did not complete the forbidden act out of fear of Allah?

Penetrating a woman in the anus is forbidden and is considered one of the major sins. The perpetrator must repent to Allah and increase their good deeds. This act does not result in the divorce of the wife, but its perpetrators are punished. If they do not desist, they are separated. Vowing to abandon this act is called a vow of obstinacy (nadhr al-lajaj), and if it is not fulfilled, it requires an expiation for breaking an oath (kaffarat yamin), or the choice between fulfilling the vowed act or offering expiation.