to show respect.

What did the Prophet (saw) do after reciting Surat An-Najam?
 Narrated `Abdullah:                     The Prophet recited Surat An-Najam and prostrated, and there was nobody who did not prostrate then except a man whom I saw taking a handful of pebbles, lifting it, and prostrating on it. He then said, "This is sufficient for me." No doubt I saw him killed as a disbeliever afterwards.