faith is this declaration. Furthermore, Sahīh Muslim records:

“The Prophet, may Allah bless him and grant him peace, said: ‘Ubayy, do you know which verse in the Book of Allah is the greatest?’ He replied: ‘Allah—there is no deity worthy of worship except Him, the Ever-Living, the Sustainer of all.’ The Messenger of Allah, may Allah bless him and grant him peace, then said: ‘May you rejoice in your knowledge, Abū al-Mundhir!’”

In this authentic hadith, he stated that this is the greatest verse in the Quran, and in the other, that this declaration is the highest of the branches of faith. This is the utmost excellence, for the whole religion is encompassed by the Quran and faith. Since it is the greatest in the Quran and the highest in faith, its supreme merit is established.

Moreover, affirming Allah’s oneness is the foundation of faith. It is the declaration that distinguishes the people of Paradise from the people of the Fire, and it is the price of Paradise. No one’s Islam is valid without it. Whoever’s last words are ‘There is no deity worthy of worship except Allah’ will enter Paradise. Every sermon that contains no testimony of faith is like a severed hand. It thus occupies the position of a root, while praising and glorifying Allah occupy that of branches.

Furthermore, it is prescribed as an expression of magnification, to be proclaimed aloud, and on momentous occasions—for example, in the call to prayer, in which voices are raised, and when ascending to high places, because of the height and elevation involved. The declaration ‘Allah is the Greatest’ is proclaimed aloud in the prayers, and it is prescribed on the festivals.