The Messenger of Allah ﷺ said, "Supplication is worship itself." Then he recited, "And your Lord said, 'Call upon Me, I will respond to you'" [Ghafir 40:60].
حدثنا علي بن محمد حدثنا وكيع عن الأعمش عن ذر بن عبد الله الهمداني عن يسيع الكندي
قال رسول الله ﷺ إن الدعاء هو العبادة ثم قرأ {وقال ربكم ادعوني أستجب لكم}
[Sahih] Abu Dawud narrated it in the Book of Prayer, Chapter on Supplication, no. 1479, from the hadith of Dhirr through this chain. Tirmidhi said, in no. 2969, "Hasan sahih." Ibn Hibban graded it sahih, no. 2396, as did Hakim, 1/490–491, and Dhahabi. Amash was corroborated by Mansur.