When the sun has risen high and there is heat in its rays, the performance of 2,4, 6,8 or 12 rakaats is called Namaaz-e-Chaast. This is full of countless rewards.
The Traditions says that the performance of 2 rakaats wipes away all ones sins. There are 360 joints in our body and to pay Sadakah for each is Wajib (obligatory) The 2 rakaaats is enough to pay all the Sadakah. Performance of 4 rakaats places the performer's name among the Abids and is the Sunnat of Saliheen and promise the performer protection until the evening. The performer of 6 rakaats is relieved of his day's worries. Performance of 8 rakaats places his name among the Parhezgaars and the performer of 12 rakaats ensures a Golden Mansion or castle for himself in Paradise. (Ref : Tirmizi, Ibne Majah, Ahmad and Abu Yala)
Rasulullah is reported to have said, 'Whoever offers 2 Rakaats of Salat al-Dhuhaa, all his sins will be forgiven even though they are as much as the foam of the sea.' (Ibid)
It is reported that Sayyidna Aaisha (Radhiallaahu Anha) used to perform 8 Rakaats of Salat al-Dhuhaa. She said that even if her parents arose from the grave, she would not leave Salat al-Dhuhaa to go and meet them. (Ibid).
'Salat al-Dhuhaa consists of 2 - 12 Rakaats and it is preferable to perform 8 Rakaats.' (Raddul Mukhtaar vol.1 pg.505)
The Prophet (sallallahu alaiyhi wassallam) is reported to have said that Whoever prayed twelve rakaats at the time of Chasht, then Allah will, as reward, prepare a palace of gold for him in Paradise. [Mishkat, Tirmizi, Ibn Majah]