Musnad Ahmad 658:49

'Affan narrated to us, Muhammad bin Talhah narrated to us, from Talhah bin Musarrif, from 'Abd al-Rahman bin 'Awsajah, from al-Bara' bin 'Azib, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever grants a gift of silver, or a gift of milk, or guides someone along a path, it is like the freeing of a soul. And whoever says: 'There is no god but Allah alone, He has no partner, to Him belongs the dominion, and to Him belongs the praise, and He is capable of all things,' it is like the freeing of a soul." He said: And he used to go from one side of the row to the other, straightening their chests and their shoulders, saying: "Do not differ, lest your hearts differ." He said: And he used to say: "Indeed, Allah and His angels send blessings upon the first rows." And he used to say: "Beautify the Quran with your voices."