'Abdallah b. Mas'ud said

Before we went to Abyssinia we used to greet Allah's Messenger ﷺ when he was engaged in prayer and he would respond to us, but when we returned from Abyssinia I came to him and found him praying. I greeted him and he did not respond to me, but when he finished his prayer he said, “Allah creates new commands as He wishes, and one of them is that you must not talk during prayer.” He then returned my greeting and said, “Prayer is solely for the purpose of reciting the Qur’an and making mention of Allah, so when you are engaged in it let that be what occupies your attention.” Abu Dawud transmitted it.