‘Abdullāh Ibn Shaqīq said, “The only action that the Prophet’s (May Allāh praise him and Peace be upon him) companions consider it kufr (disbelief) to abandon was Ṣalāt .”
Allāh, Exalted is He, says, “But there came after them successors who neglected prayer and pursued desires; so, they are going to meet evil” [Maryam: 59]. Al Qurtubī mentioned in his tafsīr (Qur`ānic exegesis) the words of Imam Aḥmad that somebody who abandons Ṣalāt has disbelieved to the extent that it takes him out of the fold of Islam. [This was mentioned by Ibn Al-Qayyim in Kitāb Al-Ṣalāt (the Book of Prayer)].