‘Abdullāh b. Shaqīq Al-‘Uqaylī – Allāh have mercy on him – said:

The Companions of Allāh’s Messenger – Allah’s praise and peace be upon him – did not consider the leaving of any action to be kufr (unbelief), except the prayer (ṣalāh).

Al-Tirmidhī, Al-Sunan ḥadīth 2622. Graded ṣaḥīḥ by Al-Albānī in his edition of Sunan Al-Tirmidhī.