Sayyiduna Ibn Mas'ud (may Allah be pleased with him) narrates that before going to the land of Abyssinia, in the beginning, we used to greet the Prophet (peace and blessings be upon him) during prayer (and he would respond to us), but when we returned from Najashi's place and greeted the Prophet (peace and blessings be upon him), he did not respond. At this, I began to worry about both distant and near matters. When the Prophet (peace and blessings be upon him) finished the prayer, I asked him about this. The Prophet (peace and blessings be upon him) replied, "Allah does whatever He wills. In this matter, Allah has decided that we should not speak during prayer."