According to which text, Ashoka distributed portions of the Buddha's relics to every important town and ordered the construction of stupas over them?

Ashokavadana

According to a Buddhist text known as the Ashokavadana, Asoka distributed portions of the Buddha’s relics to every important town and ordered the construction of stupas over them. By the second century BCE a number of stupas, including those at Bharhut, Sanchi and Sarnath, had been built.