Is the husband's permission required for Salatul Tahajjud and the regular Sunnah prayers, similar to voluntary Hajj and fasting? Is permission required each time? What is the ruling on stipulating this in the marriage contract, and is it binding forever? What if the husband grants permission later? Does that affect the contract or make him sinful?

A woman is not required to seek her husband's permission for supererogatory prayers (nafl) and night vigil (tahajjud) due to their short duration, unlike fasting and Hajj. It is not permissible for a husband to stipulate that his wife should not perform supererogatory acts of worship except with his permission, as this is a void condition and holds no benefit for the husband. However, it is permissible to interrupt a wife's supererogatory prayer for the husband's right, because his right is obligatory and takes precedence over supererogatory acts.