Question: If a person performs Sawm and Salaah only during Ramadaan then after Ramadaan he abandons Salaah, is his fast valid?
Answer: Salaah is one of the pillars of Islaam. It is the most important pillar of Islaam after the Shahaadah (Testimony of Faith). It is an individual obligation. Whoever abandons it out of negligence or laziness is a Kaafir (a disbeliever)… read more here.