5.6

Translation by Swami Sivananda
6 The three letters of AUM, if employed separately, are mortal; but when joined together in meditation on the total Reality and used properly on the activities of the external, internal and intermediate states, the knower trembles not. 

Translation by Max Mueller
6. The three Mâtrâs (A + U + M), if employed separate, and only joined one to another, are mortal; but in acts, external, internal, or intermediate, if well performed, the sage trembles not.