Manava Dharmashastra 4.110

4.110

eka uddiśyate yasmiṃstat'ekoddiṣṭaṃ' navaśrāddham | tatra 'niketanaṃ' nimantraṇaṃ pratigṛhya, aṅgīkṛtya tryahamanadhyāya āmantraṇātprabhṛti | evaṃ 'rājñā' candramāstasya sūtakaṃ, rāhuṃ pratyamṛtasravaṇam | 'ca'śabdātsūryasya ca | athavā janapadeśvarasya 'rājñaḥ sutakaṃ' putrajanmotsavaḥ | rāhoḥ sūtakaṃ candrasūryayoruparāgaḥ, grahaṇamiti prasiddham |

Medhātithi’s commentary (manubhāṣya):
The ‘Unitary Rite’ is that which is offered to a single ancestor; i.e., the fresh funeral rite (that which is performed after death);—having ‘accepted’—agreed to—‘invitation’ at that rite, it becomes an occasion unfit for study, for three days, counting from the day of the invitation.

Similarly, when ‘of the King’—i.e., of the Moon—there is ‘impurity,’ i.e., pouring of nectar towards Rāhu. ‘Also’ in this case, is meant to include the Sun also.

Or, the ‘impurity of the King’ may mean the rejoicings accompaying the birth of a son to the King, the ruler of men; and the ‘impurity of the Rāhu,’ for the eclipses of the Sun and the Moon, known as ‘grahaṇa,’ ‘catching.’—(110)