Bhagavatapurana 1.3.10

1.3.10

pañcamaḥ kapilo nāma siddheśaḥ kālaviplutam /
provācāsuraye sāṅkhyaṃ tattvagrāmavinirṇayam //

10. The fifth Avatara was as Kapila, the Lord of Siddhas, who taught Asuri (the brahmana), the Sankhya sastra, obscured by time, which leads to a correct and conclusive understanding of the Tattvas (fundamental principles).