Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates: Previously, during prayer, we used to greet the Prophet Muhammad (peace and blessings be upon him) with salam, and he would reply to our salam. The narrator says: This used to happen during prayer. Then, when we came from the land of Abyssinia (to Madinah Munawwarah), I greeted the Prophet Muhammad (peace and blessings be upon him) with salam while he was praying, but he did not reply to me. Various apprehensions came to my mind. I sat down until the Prophet Muhammad (peace and blessings be upon him) completed his prayer. Then I submitted to him: Previously, you used to reply to our salam. The Prophet Muhammad (peace and blessings be upon him) said: Allah, the Exalted, can make a new decision as He wills, and He has made a new decision regarding this matter: Do not speak during prayer.