Apastambadharmasutra 2.2.3.13

2.2.3.13

teṣāṃ mantrāṇām upayoge dvādaśāham adhaḥśayyā brahmacaryaṃ kṣāralavaṇavarjanaṃ ca /

Whilst learning the sacred formulas (to be recited during the performance) of those (burnt oblations and Bali-offerings, a householder) shall sleep on the ground, abstain from connubial intercourse and from eating pungent condiments and salt, during twelve days.