Numan bin Basheer (R.A) narrates from Rasool-Allah (P.B.U.H) “Duaa is ibadat.” Then Hazrat Muhammad (P.B.U.H) read this ayat .
(Tirmizi, Abu Dawod, and Ibn-e-Majah)

Abu Hurairah (R.A) narrates from Rasool-Allah (P.B.U.H) “In the court of Allah, there is no greater thing than duaa” (Ibn-e-Majah).

Abdullah bin Umar (R.A) narrates from Rasool-Allah (P.B.U.H) ” Among whatever has been descended and whatever has not been descended Duaa is beneficial of all. Oh people of Allah! Assume Duaa a must for yourselves. (Tirmizi)

Abdullah bin Umar (R.A) from Rasool-Allah “For whoever the door of duaa opened, for him the doors of mercy are opened. Whatever duaa is asked from Allah the best duaa is for well-being and safety among them.” (Tirmizi)

Abu Hurairah (R.A) narrates from Rasool-Allah (P.B.U.H) “Allah is extremely displeased with the person who doesn’t do duaa to Allah”. (Tirmizi)