Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "Learn the Qur'an and recite it; you will be rewarded with ten good deeds for every letter. Listen, I do not say that Alif-Lam-Mim (is one letter); rather, I say: Alif, and Lam, and Mim (are separate letters)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8617