What is the ruling on someone who is praying a Sunnah prayer when the iqamah for congregational prayer is called: Should he interrupt his prayer to join the fard prayer, or should he hasten, or should he complete his prayer as usual? And is it true that for every 12 rak'ahs of supererogatory prayers, a house is built in Paradise, or is this reward for whoever consistently observes this Sunnah in general?

Gaining a house in Paradise is contingent upon performing twelve rak'ahs during the day or night. The one who voluntarily performs these rak'ahs will attain a house each time they pray this number. It is said that these rak'ahs are the regular Sunnah prayers (al-rawatib) or other voluntary prayers. If a person misses the Sunnah of Dhuhr, they can make it up or perform an equivalent voluntary prayer to attain the reward.