Apastambadharmasutra 2.4.9.13

2.4.9.13

atha-apy [udāharanti / (ś) aṣṭau grāsā muner bhakṣaḥ# ṣoḍaśa-araṇyavāsinaḥ / dvātriṃśataṃ gṛhasthasya-[aparimitaṃ brahmacāriṇaḥ // ( K bhakṣyāḥ )
(ś) āhitāgnir anaḍvāṃś ca brahmacārī ca te trayaḥ / [aśnanta eva [sidhyanti na-eṣāṃ siddhir [anaśnatām iti //

Now they quote also (the following two verses):
'Eight mouthfuls are the meal of an ascetic, sixteen that of a hermit living in the woods, thirty-two that of a householder, and an unlimited quantity that of a student. An Agnihotrin, a draught-ox, and a student, those three can do their work only if they eat; without eating (much), they cannot do it.'