One verse

Srimad Bhagavatam 11.18.8

11.18.8

अग्निहोत्रं च दर्शश्च पौर्णमासश्च पूर्ववत् । चातुर्मास्यानि च मुनेराम्नातानि च नैगमै: ॥ ८ ॥

agnihotraṁ ca darśaś ca paurṇamāsaś ca pūrva-vat cāturmāsyāni ca muner āmnātāni ca naigamaiḥ

agni-hotram
the fire sacrifice
ca
also
darśaḥ
the sacrifice performed on the new moon day
ca
also
paurṇa-māsaḥ
full moon sacrifice
ca
also
pūrva-vat
as previously, in the gṛhastha-āśrama
cātuḥ-māsyāni
the vows and sacrifices of cāturmāsya
ca
also
muneḥ
of the vānaprastha
āmnātāni
enjoined
ca
also
naigamaiḥ
by expert knowers of the Vedas.

The vānaprastha should perform the agnihotra, darśa and paurṇamāsa sacrifices, as he did while in the gṛhastha-āśrama. He should also perform the vows and sacrifices of cāturmāsya, since all of these rituals are enjoined for the vānaprastha-āśrama by expert knowers of the Vedas.