Bhagavad Gita 17.28
Whatever is done without faith, whether it be sacrifice, austerity, gift, or anything else, is called Asat (meaning "Unreal"), for it is the negation of Sat, O Arjuna! Such an act has no significance, here or hereafter.
अश्रद्धया हुतं दत्तं तपस्तप्तं कृतं च यत्।असदित्युच्यते पार्थ न च तत्प्रेत्य नो इह॥aśraddhayā hutaṃ dattaṃ tapastaptaṃ kṛtaṃ ca yat|asadityucyate pārtha na ca tatpretya no iha||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).