Messenger of Allah ﷺ said, "The Um (substance) of the Qur'an is the seven oft-repeated verses (Al- Mathaini) and is the Great Qur'an (i.e. Surat-al-Fatiha). (Using translation from Bukhārī 4704)
"أُمُّ الْقُرْآن هى السبعُ المثانِي والقُرْآن العظِيمُ".