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.
Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura has given a detailed explanation of the four rituals mentioned here, namely agnihotra, darśa, paurṇamāsa and cāturmāsya. The conclusion is that everyone should simply chant Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare and avoid the difficult entanglement of Vedic ritualistic ceremonies. If one neither chants Hare Kṛṣṇa nor performs such rituals, one certainly becomes a pāṣaṇḍī, an atheistic fool.