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 knowledge pertaining to acts of worship as much as necessary. It is a serious misstep to ignore the knowledge of fiqh and to be busy proving Allah’s existence instead. 

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 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 because while iman is so precious, kufr, its opposite, is so evil.

It is fard-i ‘ayn to study the knowledge of kalam, which explains the facts 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 may deviate onto wrong paths and become zindiqs (atheists who pretend to be Muslims).

Islamic scholars state:
Committing grave sins is milder 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)

If one believes in Allah and the next world but does not believe in even 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]

 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 disbelieve the prophethood of Muhammad ‘alaihis-salam, they are disbelievers. Similarly, if a Muslim denies one of the six fundamentals expressed in the Amantu, for example, belief in qadar, they become disbeliever and all their 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.

Question: There are people and books trying to prove only the existence of Allah. Some people do not read any books other than these. Does it suffice to say only “Allah exists” and to know His existence in order to be a Muslim?
ANSWER
Some non-Muslims can easily understand the existence of a Creator by looking at the universe and say that Allah exists. However, it is a condition to believe in the six fundamental principles expressed in the Amantu in order to be a Muslim. A person who disbelieves even one of them cannot be a Muslim. Constantly reading the books proving the existence of Allah results in doubts in one’s heart when facing things of which the hidden reasons behind we cannot know, which causes disbelief. Writers who are busy with these activities do not abstain from using such words as “Islamic thought” or “Divine conscience” or “Allah’s view” because they do not know aqaid or fiqh. It is easy for them to fall into disbelief. Readers of such books, similarly, cannot know the statements which lead them to disbelief. Therefore, it is necessary to learn fiqh and aqaid as well.

After correcting their faith according to the creed of Ahl as-Sunnah, a believer in Allah must know fiqh thoroughly. If they do not, they perform acts of worship incorrectly, and they will be of no use. Moreover, they may perform bid'ah. Their incorrect acts of worship and bid’ah may lead them to disbelief.

In order to be a true Muslim, it is necessary to learn Sufism and ethics of Islam. If one does not know fiqh and Islamic ethics and not believe in accordance with Ahl as-Sunnah principles, it is of no value even if one shouts out “Allah exists and one” from day to night and proves His existence with 99 proofs.

A scholar named Ibn Sakka used to place a high value on reasoning and 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)

Today, those who try to prove the existence of Allah with proofs are not different from Ibn Sakka. They consider Christianity a true religion and sees priests pious.  Can a non-Muslim be pious? All of Ah al-Kitab are disbelievers. A Qur’anic verse says (what means):

(All disbelievers, be they Ahl al-Kitab [Jews and Christians] or polytheists, will remain in Hell forever.) [Al-Baiyinah 6]