Abdullāh b. Masʿūd said, “Everything has a peak (i.e., pinnacle) and the peak of the Qur’an is al-Baqarah.” Reference:

Sunan ad-Darimi 2179. Al-Silsilah al-Ṣaḥīḥah, 135/2.

وَعَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ أَنَّهُ قَالَ: إِنَّ لِكُلِّ شَيْءٍ سَنَامًا وَإِنَّ سَنَامَ الْقُرْآنِ سُورَةُ الْبَقَرَةِ.