Which Surah is called sulusul qur'an?

Surah Al-Ikhlas is often referred to as "Sulusul Qur'an," which means "one-third of the Qur'an." This designation highlights its profound emphasis on the concept of monotheism (Tawhid) and the oneness of Allah. The Surah encapsulates the essence of Islamic belief in a concise manner, making it significant in the teachings of Islam.