Manava Dharmashastra 6.12

6.12

parvasu yaddevatābhyo dattaṃ tacchiṣṭameva bhakṣayenna śākamūlaphalādi | śeṣamātmani yuñjīta ātmanimittamupayojayeta, ātmārthaṃ śarīrasthityarthamityarthaḥ | svayaṃ kṛtaṃ ca lavaṇaṃ na saindhavādi niṣeveta |

Having offered to the gods that most pure offering consisting of wild-growing things, he shall take to himself the remnant, as also the salt prepared by himself—(12).

Medhātithi’s commentary (manubhāṣya):
He should eat only what remains after the offerings to the gods have been made on the New and Full moon days,—and not any herbs, roots, fruits and the rest.—‘He shall take to himself the remnant’ shall use it for his own purposes, i.e., for the sustaining of his body.

He should eat only such salt as is ‘prepared by himself’ and not rock-salt &c.—(12).

‘Lavaṇam svayam kṛtam’—‘Collected from saltmarshes’ (Kullūka);—‘collected from salt or alkaline elements of trees and the like’ (Nārāyaṇa).

This verse is quoted in Mitākṣarā (on 3.46), which explains that the salt is to be collected from salt-marshes.