This article provides an edition and translation of an inscribed two-sided stela (K. 1457), discovered during the construction of a road in the northwest of Cambodia in 2019, that commemorates the endowment of a Viṣṇu temple during the reign of the ninth-century king Jayavarman III. The inscription, in Sanskrit verse except for a few lines in Khmer prose that give details of the grants made, is undated, but uses the posthumous name of Jayavarman III, namely Viṣṇuloka, whose death cannot have occurred later than 877 CE. »Syncretism« is a label often bandied about in connection with ancient Khmer religious life. In counterpoise, this epigraph alludes to Jayavarman III having attempted to drive out Buddhists and to convert his subjects into Śaivas, before being himself won over to Vaiṣṇava devotion, after his Śaiva chaplain was struck dumb and died during a debate with a priest of the temple of Cāmpeśvara, once the most famous Viṣṇu temple in the Khmer religious landscape, whose location can no longer be determined with certainty. A second faith-inspiring drama is also sketched after the first endowment: a wife of the king entered Viṣṇu's temple while menstruating and began to bleed from her breasts. K. 1457 adds nuance to our picture of the interrelations between the classical Indian religions among the Khmers, and confirms the recognition at that time of three principal religionists: Buddhists, Vaiṣṇavas, and Śaivas. Comparison with evidence for religious rivalry specifically between Śaivas and Vaiṣṇavas in different parts of the Indian sub-continent (particularly Nepal and the Tamil-speaking South) enables us to set the Cambodian evidence in a relevant context.