Narrated by Numan ibn Bashir (May God be pleased with him):

The Prophet (Peace and Blessings be Upon Him) said:

“Supplication is prayer”, and then read this verse: “And your Lord says: ‘Call on Me; I will answer your (Prayer) but those who are too arrogant to serve Me will surely find themselves in Hell – in humiliation!’” (Surah Ghafir, 40/60)

(Abu Davud, Prayer 358)