Musannaf Ibn Abi Shaybah 4889 — A man greeted with salam in prayer

Sayyiduna Abdullah (bin Mas'ud) (may Allah be pleased with him) said: Before going to the Negus (al-Najashi), we used to greet the Prophet (peace and blessings be upon him) and he would return our greeting. When we came back from the Negus, I greeted the Prophet (peace and blessings be upon him), but he did not return the greeting, and after completing the prayer he said: "Prayer has its own preoccupation."