And your Lord says, "Call upon Me; I will respond to you." Indeed, those who disdain My worship will enter Hell [rendered] contemptible.
I heard the Messenger of Allah (sallallaahu alayhi wa sallam) as saying: There is an hour during the night in which no Muslim bondman will ask Allah for good in this world and the next but He will grant it to him.
[Sahih Muslim Hadith No. 757]
Abu Burda b. Abu Musa al-Ash'ari reported:
'Abdullah b. Umar said to me: Did you hear anything from your father narrating something from the Messenger of Allah (sallallaahu alayhi wa sallam) about the time on Friday? I said: Yes, I heard him say from the Messenger of Allah (sallallaahu alayhi wa sallam) (these words): "It is between the time when the Imam sits down and the end of the prayer."
[Sahih Muslim Hadith No. 853]
Narrated An-Nu'man ibn Bashir:
The Prophet (sallallaahu alayhi wa sallam) said: Supplication (du'aa') is itself the worship.
(He then recited:) "And your Lord said: Call on Me, I will answer you" [Qur’aan 40:60].
[Sunan Abu Dawud Hadith No. 1479]