Explaining who a believer is in the sight of Allah
What is meant by Ūṣūl ad-Dīn and what is the meaning of al-Īmān ash-Sharʿī al-Manhajī according to Allah the Exalted?
Answer (Imam Wahbah az-Zuḥaylī):
Al-Īmān ash-Sharʿī is nothing but affirmation in the heart (i.e. accepting it and submitting to it) of everything that is known by necessity (without evidence or proof) of the religion of Muḥammad, may Allah bless him and grant him peace, such that the masses learn it without examination or deduction, such as Allah’s Oneness, Prophecy, the Resurrection, reward and punishment, the obligation to pray, give zakāh, perform the Ḥajj, and the unlawfulness of wine and so forth.
Generality suffices for that in which generality is accepted, such as faith in the angels, the Books and the Messengers, and detail is stipulated in that which requires detail, such as faith in Jibrīl, Mīkāʾil, Mūsā, the Torah, the Injīl and the Qurʾān, such that if someone does not affirm any one of the aforementioned matters, one has disbelieved.
In other words, one must know the five pillars of Islam: the testimony that there is no god but Allah and that Muḥammad is the Messenger of Allah, the establishment of the prayer, the giving of the zakāh, the fasting of Ramaḍān and the Ḥajj to the House for whoever is able to.
And one must know the pillars of faith: faith in Allah, His Angels, His Books, His Messengers, the Last Day and in the Decree and Predestination, the good of it and the bad of it.
The majority of the Shāfiʿīs have stipulated that whoever believes that the Message of Muḥammad, may Allah bless him and grant him peace, is exclusive for the Arabs must openly disavow every religion that contradicts the religion of Islam, and this is so that the rulings of Islam can be applied to him, not to establish his faith and so that he can be described as a believer in Allah the Exalted. Thus, if a person only declares the two testimonies of faith and has firm conviction in the generality of the Islamic Message, he is a believer according to Allah.
[Translated from Fatāwā Muʿāṣirah (Damascus: Dār al-Fikr, 1427/2006), p.263-264]
 (tn): i.e. faith according to the Revealed Law
 Ar. naẓr
 Ar. istidlāl
 (tn): i.e. a person is not a believer if they affirm the angels but denies the Jibrīl, peace be upon him is an angel, or affirms the Messengers but deny that Mūsā, peace be upon him is a Messengers, or they affirm the Book but deny that the Torah is one of the Books