In the Chandogya Upanishad, the boy Satyakama asks his mother about his lineage. She tells him: “I was very busy serving many people when I was young, and I had you.” She says that she knows nothing about his lineage.
He goes to the teacher Gautama and repeats her words to him. Gautama answers: “No non-brahmin could speak like this.” He accepts Satyakama as a student, “as you have not deviated from truth.”