All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
This Hadeeth is reported in the book of Imaam Muslim and others, on the authority of Umm Habeebah .
It appears –Allah knows best –that whenever a Muslim prays this number of Rak'ahs in one single day, Allah builds a house for him in Paradise; the houses are multiplied according to the multiplication of the days [in which one performs those Rak’ahs].
Shaykh Ibn ‘Uthaymeen was asked the following question in Fataawa Noorun ‘Ala Ad-Darb:
“The Prophet said: “Whoever prays twelve Rak'ahs other than the obligatory prayer, Allah builds a house for him in Paradise." My question is: is the one who prays them and is continuous in praying them every day, will a house be built for him. For example, if he prays them for three consecutive days, will three houses be built for him, or what?”
He replied, said:
“Yes, whoever prays twelve Rak'ahs in a day and night; Allah will build for him a house in Paradise for the twelve optional prayers that he had prayed. Therefore, if he prays them constantly, then for every day that goes by (in which he prays these twelve), a house will be built for him in Paradise.” [End of quote]
Shaykh ibn ‘Uthaymeen said in his commentary on Saheeh Muslim:
“The apparent meaning of the Hadeeth indicates that it is not required to maintain these Rak'ahs daily (in order to get this reward); and that if a person prays them one single day, then Allah will built for him a house in Paradise.” [End of quote]
Allah knows best.