What is the ruling on deferring all or part of the mahr (dower), what are its effects and rulings, is it permissible for the wife to deny herself to her husband because of it, and what are the views of the four schools of thought on this matter?

The default rule for the mahr (dowry) is that it should be specified at the time of marriage, clarifying both its immediate and deferred portions. If the mahr is not specified, the marriage is valid by scholarly consensus, and the wife is entitled to a mahr al-mithl (a dowry equivalent to that of women of her status). The deferred portion of the sadaq (dowry) is a debt owed by the husband and is a right of the wife. It is permissible to defer all or part of the sadaq according to the agreement of the four madhhabs, though it is considered disliked by the Malikis. Deferment has three cases:

1. Deferment to a known time: This is permissible by consensus of the jurists. 2. Deferment to an unknown time: This is not permissible, and the deferment is void according to the four madhhabs. The mahr becomes immediately due according to the majority of scholars. According to the Shafi'is, it invalidates the deferment, and she is entitled to a mahr al-mithl. 3. Absolute deferment: The preponderant opinion is that such deferment is valid, and the woman is not entitled to demand it except upon death or separation. This is the view chosen by Ibn Taymiyyah and Ibn 'Uthaymeen. It is permissible for the woman to refuse to surrender herself (to conjugal relations) before receiving the immediately due, non-deferred mahr.