Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: I met Sayyiduna Abu Dharr (may Allah be pleased with him) and said: O uncle, I am in need of benefiting from your knowledge. He said: I asked the Messenger of Allah (peace and blessings be upon him) just as you have asked me, and he (peace and blessings be upon him) said: "If you pray two rak'ahs of Duha, you will not be recorded among the heedless; if you offer four rak'ahs, you will be recorded among the doers of good (muhsinin); if you pray six rak'ahs, you will be recorded among those who stand in devotion; if you pray eight rak'ahs, you will be recorded among the successful; if you pray ten rak'ahs, no sin will be recorded against you that day; and if you pray twelve rak'ahs, Allah will build a house for you in Paradise."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4906