Not that fast br. Improv.
Here is how believer is defined;
One who says:
Your God is Allah alone [The cow 2:163]
Muhammad is Allah's Messenger [ Victory 48:29]
[Shakir 3:84] Say: We believe in Allah and what has been revealed to us, and what was revealed to Ibrahim and Ismail and Ishaq and Yaqoub and the tribes, and what was given to Musa and Isa and to the prophets from their Lord; we do not make any distinction between any of them, and to Him do we submit.
[Shakir 2:285] The messenger believes in what has been revealed to him from his Lord, and (so do) the believers; they all believe in Allah and His angels and His books and His messengers; We make no difference between any of His messengers; and they say: We hear and obey, our Lord! Thy forgiveness (do we crave), and to Thee is the eventual course.
[Shakir 2:286] Allah does not impose upon any soul a duty but to the extent of its ability; for it is (the benefit of) what it has earned and upon it (the evil of) what it has wrought: Our Lord! do not punish us if we forget or make a mistake; Our Lord! do not lay on us a burden as Thou didst lay on those before us, Our Lord do not impose upon us that which we have not the strength to bear; and pardon us and grant us protection and have mercy on us, Thou art our Patron, so help us against the unbelieving people
[Shakir 60:12] O Prophet! when believing women come to you giving you a pledge that they will not associate aught with Allah, and will not steal, and will not commit fornication, and will not kill their children, and will not bring a calumny which they have forged of themselves, and will not disobey you in what is good, accept their pledge, and ask forgiveness for them from Allah; surely Allah is Forgiving, Merciful.
[Shakir 17:22] Do not associate with Allah any other god, lest you sit down despised, neglected.
[Shakir 17:23] And your Lord has commanded that you shall not serve (any) but Him, and goodness to your parents. If either or both of them reach old age with you, say not to them (so much as) "Ugh" nor chide them, and speak to them a generous word.
[Shakir 17:24] And make yourself submissively gentle to them with compassion, and say: O my Lord! have compassion on them, as they brought me up (when I was) little.
[Shakir 17:25] Your Lord knows best what is in your minds; if you are good, then He is surely Forgiving to those who turn (to Him) frequently.
[Shakir 17:26] And give to the near of kin his due and (to) the needy and the wayfarer, and do not squander wastefully.
[Shakir 17:27] Surely the squanderers are the fellows of the Shaitans and the Shaitan is ever ungrateful to his Lord.
[Shakir 17:28] And if you turn away from them to seek mercy from your Lord, which you hope for, speak to them a gentle word.
[Shakir 17:29] And do not make your hand to be shackled to your neck nor stretch it forth to the utmost (limit) of its stretching forth, lest you should (afterwards) sit down blamed, stripped off.
[Shakir 17:30] Surely your Lord makes plentiful the means of subsistence for whom He pleases and He straitens (them); surely He is ever Aware of, Seeing, His servants.
[Shakir 17:31] And do not kill your children for fear of poverty; We give them sustenance and yourselves (too); surely to kill them is a great wrong.
[Shakir 17:32] And go not nigh to fornication; surely it is an indecency and an evil way.
[Shakir 17:33] And do not kill any one whom Allah has forbidden, except for a just cause, and whoever is slain unjustly, We have indeed given to his heir authority, so let him not exceed the just limits in slaying; surely he is aided.
[Shakir 17:34] And draw not near to the property of the orphan except in a goodly way till he attains his maturity and fulfill the promise; surely (every) promise shall be questioned about.
[Shakir 17:35] And give full measure when you measure out, and weigh with a true balance; this is fair and better in the end.
[Shakir 17:36] And follow not that of which you have not the knowledge; surely the hearing and the sight and the heart, all of these, shall be questioned about that.
[Shakir 17:37] And do not go about in the land exultingly, for you cannot cut through the earth nor reach the mountains in height.
[Shakir 17:38] All this-- the evil of it-- is hateful in the sight of your Lord.
[Shakir 17:39] This is of what your Lord has revealed to you of wisdom, and do
I hope you have read and understood Qur'an.
Those who Believe in Allah his last messenger and 3 other basic principls of Islam are believers.