NIST seems to have it as a guideline for memorised secrets:
Verifiers SHOULD NOT impose other composition rules (e.g., requiring mixtures of different character types or prohibiting consecutively repeated characters) for memorized secrets. Verifiers SHOULD NOT require memorized secrets to be changed arbitrarily (e.g., periodically). However, verifiers SHALL force a change if there is evidence of compromise of the authenticator.
Any source about why changing a password regularly is not recommended?
NIST seems to have it as a guideline for memorised secrets: