Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
This statement: “Whoever relies on his wealth, it diminishes; whoever relies on his intellect, he goes astray; and whoever relies on Allah will never go astray” has no known authentic chain of transmission back to the Prophet ﷺ. It has also been attributed to Ali ibn Abi Talib, may Allah be pleased with him. Therefore, it is not correct to attribute it to the Prophet ﷺ as a hadith.
As for reason in Islam, it has a great status, including the following:
It is a condition for being legally accountable; a person is not held responsible for commands and prohibitions unless he possesses sound reason.
The Shariah came to preserve the intellect, and therefore it prohibited wine, drugs, and everything that corrupts it.
Using reason correctly helps in understanding the texts of the Qur’an and Sunnah, reflecting upon the proofs of monotheism and faith, and distinguishing between truth and falsehood.
Allah تعالى has condemned those who neglected to benefit from their intellect in recognizing the truth. He says:
﴿And they will say, “If only we had listened or reasoned, we would not have been among the companions of the Blaze.”﴾ [Al-Mulk: 10].
However, reason does not independently establish religious legislation, nor is it given precedence over authentic textual evidence. A Muslim takes his religion from the Book of Allah, the Sunnah of His Messenger ﷺ, and what the early generations of the Muslim community unanimously agreed upon. There is no genuine contradiction between sound revelation and sound reason. If a person appears to find that an authentic text contradicts reason, then the problem is either in his understanding of the text or in his rational premises, not in revelation.
As for ijtihad, reason is used in it to understand the texts, reconcile them, determine their implications, and apply rulings to particular circumstances, in accordance with the principles and rules of the Shariah. It is not used to oppose the texts or reject them merely because the intellect has not understood their wisdom.
Therefore, the correct position is neither to abolish the use of reason nor to give it precedence over revelation. Rather, reason should be used for the purpose Allah has assigned to it, while being guided by the Qur’an and Sunnah. Reason is a means of understanding the Shariah, not a judge over it.
And Allah تعالى knows best.