Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.109.
Allah has commanded people to call upon Him humbly and sincerely, promising them He will respond to their prayers and fulfil their needs.
Nu’man b. Bashir reported that the Prophet, peace be upon him, said, “Verily supplication is worship.” Then he recited the Qur’anic 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 humiliated in Hell!” Qur’an 40.60. This is reported by Ahmad and Sunan.
‘Abdar Razzaq reported from Al-Hasan that the Companions asked the Prophet, peace be upon him, “Where is our Lord?” At this Allah sent down the following verse of the Qur’an, “When My servants ask you (O, Muhammad) concerning Me, I am indeed close to them. I listen to the prayer of every supplicant when he calls upon Me.” Qur’an 2.186
Abu Hurairah reported, “The Prophet, peace be upon him, said, “Nothing is more dear to Allah than one’s supplication to Him.” (Tirmizhi and Ibn Majah)
Abu Hurairah also reported, “The Prophet, peace be upon him, said, ‘Whoever wants Allah to answer his prayers during difficult times, should supplicate to Him more and more in times of ease.” (Tirmizhi)
Abu Ya’la related from Anas that the Prophet, peace be upon him, reporting from his Lord said, “Allah said, ‘There are four characteristics, of which one is Mine, one yours, one common between Me and you, and one is common between you and My other servants. The one that is Mine is that you shall not associate any other god with Me, the one that is for you is that when you do a good deed I shall reward you for it, the one that is common between Me and you is that when you supplicate I shall respond to your supplications, and the one that is common between you and My other servants is that you should like for them what you like for your own selves’.”
In a sound hadith the Prophet, peace be upon him, said, “Allah’s wrath is on the one who does not call upon Him for help.” ‘Aishah reported, “The Prophet, peace be upon him, said, ‘Precautions are of no avail against the decree of Allah, but the supplication benefits in the case of a calamity that strikes or is about to strike. And when a calamity descends the supplication intercepts it and holds it at bay until the Day of Resurrection’. (Reported by Al-Bazar, At-Tabrani, and Al-Hakim, who says its chain of authorities is sound)
Salman Al-Farisi reported that the Prophet, peace be upon him, said, “Nothing can avert the decree of Allah except supplication, and nothing increases life except virtuous deeds.” (Tirmizhi)
Abu ‘Awanah and Ibn Hibban reported that the Prophet, peace be upon him, said, “When one of you supplicates, he should ask Allah for something important and great, for nothing is difficult for Allah.”