Al-Qasim bin Abd al-Rahman narrates this saying of Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him): Whoever abandons the prayer commits disbelief.
Al-Qasim did not hear from Ibn Mas'ud.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 1638