Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.031B.

The minimum number of rak’ah to be prayed is two, as was mentioned in the hadith of Abu Zharr. The most that the Prophet sallallahu alehi wasallam performed was eight rak’at, whereas, the most he mentioned was twelve rak’at. Some people, such as Abu Ja’far at-Tabari, al-Mulaimi, and ar-Ruwyani, who subscribes to the Shafi’ school, say there is no maximum limit to the number of rak’at that one may perform for duha.

Al-‘Iraqi says, in the commentary on Sunan at-Tirmizhi: “None of the companions or followers are known to have restricted it to twelve rak’at.” As-Syuti agrees with it.

Sa’id ibn Mansur records that al-Hassan was asked: “Did the companions perform it?” He answered: “Yes . . . some of them would pray two rak’at and some of them would pray four rak’at. And some of them would continue until half the [early] day [had passed].”

Ibrahim an-Nakha’i reports that al-Aswad ibn Yazid was asked: “How many rak’at are to be prayed for duha?” He answered: “As many as you wish .”

Umm Hani narrates that the Prophet sallallahu alehi wasallam prayed eight rak’at of duha and made the taslim after every two rak’at. This is related by Abu Dawud with a sahih chain.

‘Aishah reports: “The Prophet sallallahu alehi wasallam would pray four rak’at for duha and would add to it whatever Allah willed.” This is related by Ahmad, Muslim, and ibn Majah.