Western Indologists say that Asuras were once good Devas that later rebelled against the Devas and became evil gods or anti-gods.
For example, Michael Witzel in his paper Autochthonous Aryans says:
The gods are depicted as engaging in constant and yearly contest with their --originally also divine-- adversaries, the Asura, a contest which the gods always win, until next time.
And many other Indologists:
Alain Daniélou states that Asuras were initially good, virtuous and powerful in Indian mythology. However, their nature gradually changed and they came to represent evil, vice and abuse of power. In Shiva Purana, they evolved into anti-gods and had to be destroyed because they threatened the gods.
A much-studied hymn of the Rigveda states Devav asura (Asuras who have become Devas), and contrasts it with Asura adevah (Asuras who are not Devas). - Wikipedia
Is there any evidence from Smriti, like the above mentioned Shiva Purana reference, that says that Asuras were once Devas who rebelled?