BG Chap 17 - Asat - not truth

Any sacrifice, charity or penance or other acts such as praises or respect, done without faith is called asat, since it bears no result in this world or in the next life. Such acts without faith do not give results in the next life because they were not properly executed, nor do they give fame even in this life because such acts are condemned by the saintly. Thus all acts should be done with sāttvika faith. Those with faith in the mode of goodness, worshipping the demigods, and following eating, sacrifice and charity in goodness, can easily adopt the principles of scriptures and dedicate their acts to Lord Viṣṇu by uttering Oṁ tat sat.