Abu Dawud Book 2, Hadith Number 1499.

Chapter : The counting of praise and glorification of allah on pebbles.

Narated By Abu Hurairah : Abu Dharr said: Prophet of Allah. The wealthy people have all the rewards; they pray as we pray; they fast as we fast; and they have surplus wealth which they give in charity; but we have no wealth which we may give in charity.

The Apostle of Allah (PBUH) said: Abu Dharr, should I not teach you phrases by which you acquire the rank of those who excel you? No one can acquire your rank except one who acts like you.

He said: Why not, Apostle of Allah? He said: Exalt Allah (say: Allah is Most Great) after each prayer thirty-three times; and praise Him (say: Praise be to Allah) thirty-three times; and glorify Him (say: Glory be to Allah) thirty-three times, and end it by saying, “There is no god but Allah alone, there is no partner, to Him belongs the Kingdom, to Him praise is due and He has power over everything”. His sins will be forgiven, even if they are like the foam of the sea.