Manava Dharmashastra 3.273

3.273

pāñcayajñikaṃ yacchrāddhaṃ aharaharityuktaṃ tasya vaikalpikatvamanenocyate | udakatarpaṇaṃ yatkriyate snātvā tenaiva pitṛyajñakriyāphalaṃ prāpnoti | yaduktamekamapyāśayediti tasya nāsti niyamena kartavyatā | udakatarpaṇamavaśyaṃ kartavyam |

Medhātithi’s commentary (manubhāṣya):
The present verse sets forth an option to the daily Śrāddha that has been prescribed in connection with the ‘Five Sacrifices.’

The ‘offering of water’ that is made after bath,—by that he obtains the reward of the offering to the Pitṛs. That is, it is not absolutely necessary to do what has been said (in 3.83) regarding the feeding of at least one Brāhmaṇa and the rest of it. It is only the Water-offering that must be made.—(283).