Riyad Us-Saliheen (Gardens of the Righteous)

Chapter 207
Time for the Duha (Forenoon Optional) Prayer

1143. Zaid bin Arqam (May Allah be pleased with him) reported: I saw some people performing Duha (prayers) in the early forenoon and warned them (saying): These people must know that performing Salat a little later is better. The Messenger of Allah (PBUH) said, "The Salat of the penitent is to be observed when the young ones of camels feel the heat of the sun (i.e., when it becomes very hot).''
[Muslim].

Commentary: This Hadith confirms the opinion of those who hold that Duha prayer is different from Ishraq prayer. Ishraq prayer must be performed when the sun rises about a lance in the sky while the time for Duha prayer occurs when the hoofs of the animals begin to burn and they feel troubled with the heat of the sun. Usually the six Rak`ah performed after Maghrib prayer are called Salat-ul-Awwabin (prayer of the penitent) which is founded on a weak Hadith. In the present authentic Hadith, Duha prayer is interpreted as Salat-ul-Awwabin. Thus Salat-ul-Awwabin is in fact Duha prayer.