In its capacity as one of the most preferred devotional acts, supplication (dua’a) has been emphatically encouraged by the Holy Quran on more than one occasion, such as in the following verses: When My servants ask you concerning Me, then surely I am very near. I answer the prayer of the suppliant when he calls upon Me. So, they should answer My call and believe in Me that they may walk in the right way. (2:186)
Supplicate your Lord humbly and secretly. Surely, He does not love those who exceed the limits. (7:55)
Say: My Lord would not care for you were it not for your supplication, but you have indeed rejected the truth; so, that which shall cleave shall come. (25:77)
Your Lord says: Call upon Me, I will answer you. Surely, those who are too proud for My service shall soon enter hell abased. (40:60)
Moreover, the Holy Quran has quoted supplications from a number of prophets and righteous people who had to encounter critical situations. Due to their supplications, Almighty Allah saved them.
Supplication in its origin is a religious duty and true believers are required to pray to Almighty Allah and supplicate to Him generally, as is indicated and confirmed by the abovementioned Quranic verses and many traditions.
In his book of al-Kafi, Shaykh al-Kulayni has reported through a valid chain of authority that Sadir asked Imam Baqir (AS), “Which devotional act is the best?”
The Imam (AS) answered: In the sight of Almighty Allah, nothing is better than asking Him and imploring Him for what He has in possession. No one is more hateful in the sight of Him than one who is too arrogant to serve Him and to implore Him for what He has in possession.
According to another validly reported tradition that is quoted by Shaykh al-Kulayni on the authority of Hammad ibn ‘Isa, Imam Sadiq (AS) has said: Always pray to (Almighty Allah) and do not consider the matter to have ended, because supplication is surely worship. Almighty Allah says, “Surely, those who are too proud for My service shall soon enter hell abased. (40:60)”