Points of Benefit: The Duha Prayer

Shaykh Ibn Baaz said:

Ishraaq prayer is Duha prayer done at the beginning of its time.

Majmoo’ Fataawa al-Shaykh Ibn Baaz, 11/401

The time of Duha prayer is from the time when the sun has risen to a certain height, until just before the time for Zuhr prayer.

Shaykh Ibn ‘Uthaymeen defined it as being from a quarter of an hour after the sun has risen until ten minutes before Zuhr prayer.

Al-Sharh al-Mumti’, 4/122

So all of this period is the time for Duha prayer. It is better to pray it after the sun’s heat has become intense, because the Prophet (peace and blessings of Allaah be upon him) said: “It is preferable to offer Duha prayer when the sun’s heat has become so intense that even the young of the camels feel it.” Narrated by Muslim, 748

Ibn Baaz: Majmoo’ Fataawa, 11/395
The scholars defined this as being when one quarter of the day has passed, i.e., halfway between sunrise and Zuhr prayer.
See al-Majmoo’ by al-Nawawi, 4/36; al-Mawsoo’ah al-Fiqhiyyah, 27/224 .
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.