Question: Some people are spending their lifetimes endeavoring to prove the existence of Allah. Providing such an argument, “Since the ultimate purpose is iman (faith), busying ourselves with proving the existence of Allah is better than busying ourselves with acts of worship and the knowledge of fiqh,” they say that it is necessary to strengthen one’s faith by way of observing the anatomies of plants, humans, and animals at all times. Is it appropriate for a believer in Allah to be busy with such things at all times?
ANSWER
It is never appropriate. One who believes in Allah has to know His Attributes as well. If His Attributes are not known or are known incorrectly, then one is not considered to have belief in Allah. If one believes in Allah with His Attributes, it becomes fard on one to learn the tenets pertaining to religious practices as much as necessary. It is a serious misstep to ignore the knowledge of fiqh and to be busy proving Allah’s existence instead.

[fiqh: knowledge dealing with what Muslims must do and must not do, actions, deeds, acts of worship; tenets pertaining to religious practices.]

It is declared in hadith-i sharifs:

(The capital of faith is fiqh.) [Daylami]

(Learning the knowledge of fiqh is fard on every Muslim.) [Imam-i Mawardi]

(The basic pillar of the religion is fiqh.) [Bayhaqi]

The knowledge of fiqh is learned from the books of ‘ilm-i hal (books teaching about Islam, its tenets, and acts of worship) that have been prepared accurately in accordance with the naql (conveying the religious knowledge that has been communicated by Islamic scholars without making any changes). After correcting the faith according to the creed of Ahl as-Sunnah, Muslims must perform acts of worship, which are requirements of faith, compatibly with such an ‘ilm-i hal book. Additionally, they must avoid deeds and words that cause them to lose their faith.

It is fard-i ‘ayn to study the knowledge of kalam, which explains the tenets pertaining to faith, enough to prove it by religious and scientific knowledge and to explain it to heretical or irreligious people. To learn more is necessary only for savants, but not permissible for others. If others learn more, they will deviate onto wrong paths and become zindiqs (atheists who pretend to be Muslims).

Islamic scholars state:
Committing grave sins is trivial when compared with dealing with the knowledge of kalam and thus deviating. If it were known how harmful it is to deal with the knowledge of kalam before learning the creed of Ahl as-Sunnah well, you would avoid dealing with it more than you would avoid a lion. (Imam-i Shafi’i)

Those who deal with the knowledge of kalam are always in doubt. (Imam-i Ahmad)

The Messenger of Allah encouraged fiqh but prohibited kalam. (Hadiqa)

It is fard-i ‘ayn on every Muslim to learn fiqh. (Ibn ‘Abidin)

Thanks to Sufism, faith becomes firm and is not undermined by effects bringing doubts. The faith that is strengthened through mind, evidence, and proofs cannot be so firm. (Imam-i Rabbani)

It is not permissible to learn the knowledge pertaining to faith more than it is needed, for it causes religious innovations (bida') to spread. (Hindiyya)

A scholar named Ibn Sakka used to place a high value on reasoning and strive to prove everything through mind. He would prove the existence and oneness of Allah by adducing 99 proofs. In the course of time, when faced with the subjects beyond his comprehension, he began to be plagued by ever-increasing doubts. Once he put a question to Hadrat Yusuf-i Hamadani, who was then giving a religious speech at Madrasa al-Nizamiyya. However, he rebuked him saying, “Sit down! A smell of disbelief is emanating from your words.” The hidden purpose in Hadrat Yusuf-i Hamadani’s scolding came to light when Ibn Sakka went to Istanbul as an envoy where he converted to Christianity. After becoming a Christian, this time, he began to prove the Trinity by adducing 100 proofs. (F. Hadithiyya)

If one believes in Allah and the next world but does not believe in only one of the prophets, one becomes a disbeliever. The reason why it is so is that Allahu ta’ala commands us to believe in Him, but at the same time, He commands us to believe in all His prophets. As a matter of fact, the Qur'an al-karim says (what means):

(They believe in the Book revealed to you and in the Books revealed before you, in prophets, and in the Hereafter.) [Al-Baqarah 4]

Our Master the Prophet, explaining the Qur’an al-karim, defined faith (iman) as follows:
(Iman is to have belief in Allahu ta’ala, in His angels, in His books, in His prophets, in the Last Day [that is, to have belief in the Day of Qiyama, Paradise, Hell, Judgment, and Mizan] in qadar and that good and evil are from Allahu ta’ala, and in death and Resurrection. It is to bear witness that there is no god except Allah and that I am a human slave and messenger of His.) [Bukhari, Muslim, Nasai]

If one disbelieves in one of the six fundamentals expressed in the Amantu, one becomes a disbeliever. It does not suffice only to say “Allah exists." For there are many people among non-Muslims who say, "Allah exists." However, in order for them to become Muslims, they have to believe in all prophets. Since Jews and Christians disbelieved the prophethood of Muhammad ‘alaihis-salam, they became disbelievers. Similarly, if a Muslim denies one of the six fundamentals expressed in the Amantu, for example, belief in qadar, (s)he becomes a disbeliever and all his/her good deeds perish. The fundamentals of faith are certain orders of Allahu ta’ala and among the indispensable essentials of the religion. For sincere people, that is, for those who have reason, knowledge, and fairness, there is nothing more reasonable than accepting the orders of Allahu ta'ala, that is, the fundamentals of faith. The contrary is a wrong path, along which Satan, ignorance, and obstinacy guide humans toward disbelief.