Narrated Aisha (May Allah be pleased with her): Allah's Messenger (p.b.u.h.) used to pray four Rakats (units) in Duha prayer and added whatever Allah wished for him. (Muslim)
Let it be known that Ishraaq, Salaat ul-Awwabin and Duha are different names that stand for identically the same forenoon prayer. The time of this prayer starts with the sunrise and goes on until one-fourth of the day. The least number of Rakats of Duha prayer is two and the maximum is twelve. The preferable among them are four which are supported and approved by the Ahadith of the Prophet (p.b.u.h.). It may also be remembered that this prayer is a Sunnah of former messengers as they used to offer it during their times. Hence, this prayer is a Sunnah and mustahabb (desirable). As to the matter of this prayer being called a Bidah (innovation) by Umar (May Allah be pleased with him) it only alludes to the fact that if someone develops a habit of continually offering it, it may be regarded as an innovation, as the Prophet (p.b.u.h.) did not always offer it.
Narrated Zaid bin Arqam (May Allah be pleased with him) Allah's Messenger (p.b.u.h.), "The prayer of those who are penitent is offered when the young weaned camels feel the heat of the sun." (at-Tirmidhi)
This Hadith indicates that the best time of Duha prayer is just before noon.
Narrated Anas (May Allah be pleased with him) Allah's Messenger (p.b.u.h.) said, "Whoever prays twelve Rakats (units) of Duha, Allah will build a castle for him in Paradise." (at-Tirmidhi who graded it Gharib "unfamiliar, doubtful").
Narrated Aisha (May Allah be pleased with her): Allah's Messenger (p.b.u.h.) entered my house and prayed eight Rakats (units) of Duha prayer. (Ibn Hibban in his Sahih)
By: Al-Haafidh Ibn Hajar al-Asqalaanee