Praise be to Allah.
Allah is close to His slaves; he sees where they are and He knows their situation. He hears what they say and responds to their du`a (supplication). Nothing about them is hidden from Him, as He says (interpretation of the meaning):
“Truly, nothing is hidden from Allah, in the earth or in the heaven” [Aal ‘Imraan 3:5]
Allah Alone is the One Who has created us and Who provides for us; in His hand is the dominion and He is Able to do all things:
“To Allah belongs the dominion of the heavens and the earth and all that is therein, and He is Able to do all things”
[al-Maa'idah 5:17 – interpretation of the meaning]
In Allah’s hand alone is all goodness. When He calls mankind to something good in His Book or on the lips of His Messenger (peace and blessings of Allah be upon him), they should obey that command and respond to it:
“O you who believe! Answer Allah (by obeying Him) and (His) Messenger when he calls you to that which will give you life, and know that Allah comes in between a person and his heart (i.e. He prevents an evil person to decide anything). And verily, to Him you shall (all) be gathered” [al-Anfaal 8:24 – interpretation of the meaning]
Allah is Able to do all things, and He hears the supplication of His slaves. He responds to them at all times and in all places, no matter what their various needs and languages. Allah says (interpretation of the meaning):
“And when My slaves ask you (O Muhammad) concerning Me, then (answer them), I am indeed near (to them by My Knowledge). I respond to the invocations of the supplicant when he calls on Me (without any mediator or intercessor). So let them obey Me and believe in Me, so that they may be led aright
Allah has commanded us to call upon Him in secret, with humility and submission, as He says (interpretation of the meaning):
“Invoke your Lord with humility and in secret. He likes not the aggressors” [al-A’raaf 7:55]
To Allah belongs Dominion and to Him be praise, and He is Able to do all things. The heavens and the earth and everything in them glorifies Him, as Allah says (interpretation of the meaning):
“The seven heavens and the earth and all that is therein, glorify Him and there is not a thing but glorifies His Praise. But you understand not their glorification. Truly, He is Ever Forbearing, Oft‑Forgiving” [al-Israa’ 17:44]
Allah has promised Hell to those who are too arrogant to worship Him and call upon Him. He says (interpretation of the meaning):
“Verily, those who scorn My worship [i.e. do not invoke Me, and do not believe in My Oneness, (Islamic Monotheism)] they will surely enter Hell in humiliation!”[Ghaafir 40:60]
Du`a should be made to Allah in the manner that Allah and His Messenger have prescribed. For example, Allah should be called upon by His Most Beautiful Names:
“And (all) the Most Beautiful Names belong to Allah, so call on Him by them, and leave the company of those who belie or deny (or utter impious speech against) His Names. They will be requited for what they used to do” [al-A’raaf 7:180 – interpretation of the meaning]
So we may say O Most Merciful, have mercy on us, O Ever-Forgiving, forgive us, O Provider grant us provision, and so on.
When a person makes du`a , either Allah gives him what he asked for or He diverts it from him a harm that is greater than the thing he asked for, or He stores up what he has asked for, for the Hereafter. This is because Allah has commanded us to call upon Him and He has promised to respond to our call:
“And your Lord said: ‘Invoke Me [i.e. believe in My Oneness (Islamic Monotheism) and ask Me for anything] I will respond to your (invocation)’ [Ghaafir 40:60 – interpretation of the meaning]
Allah has commanded us to worship Him alone, and He has warned us against worshipping the Shaytaan. He says (interpretation of the meaning):
“Did I not command you, O Children of Adam, that you should not worship Shaytaan (Satan). Verily, he is a plain enemy to you.
And that you should worship Me [Alone Islamic Monotheism, and set up not rivals, associate‑gods with Me]. That is the Straight Path” [Yaa-Seen 36:60-61]
Calling upon anyone other than Allah to meet one’s needs, relieve distress or heal disease is insanity caused by lack of understanding:
“Say (O Muhammad): ‘Shall we invoke others besides Allah (false deities), that can do us neither good nor harm, and shall we turn back on our heels after Allah has guided us (to true Monotheism)?’” [al-An’aam 6:71 – interpretation of the meaning]
If a person calls upon one who cannot bring benefit or cause harm, who cannot command or prohibit, who cannot hear or respond, whether that is a Prophet, a Messenger, a jinn or an angel, or a star or planet or rock or tree, or one of the dead – all of that is serious wrong-doing, and a going astray from the Straight Path. It is shirk, the association of others with Allah the Almighty.
“And invoke not besides Allah any such that will neither profit you nor harm you, but if (in case) you did so, you shall certainly be one of the Zaalimoon (wrongdoers)” [Yoonus 10:106 – interpretation of the meaning]
Allah says (interpretation of the meaning):
“And who is more astray than one who calls on (invokes) besides Allah, such as will not answer him till the Day of Resurrection, and who are (even) unaware of their calls (invocations) to them
Calling upon anyone or anything other than Allah is shirk, and shirk is a great sin, indeed it is the greatest sin. Allah will forgive any sin for whomever He wills, except for shirk, as Allah says (interpretation of the meaning):
“Verily, Allah forgives not that partners should be set up with Him (in worship), but He forgives except that (anything else) to whom He wills [al-Nisaa’ 4:48]
On the Day of Resurrection, Allah will gather the mushrikeen and everyone who was worshipped instead of Him, then those who were worshipped instead of Allah will disavow those who worshipped them, and they will deny their association with Allah, as Allah says (interpretation of the meaning):
“And those, whom you invoke or call upon instead of Him, own not even a Qitmeer (the thin membrane over the date stone).
If you invoke (or call upon) them, they hear not your call; and if (in case) they were to hear, they could not grant it (your request) to you. And on the Day of Resurrection, they will disown your worshipping them. And none can inform you (O Muhammad) like Him Who is the All‑Knower (of everything).
O mankind! it is you who stand in need of Allah. But Allah is Rich (Free of all needs), Worthy of all praise”[Faatir 35: 13-15]