Skandapurana 5.127.24

5.127.24

tathā'trāsti śubhaṃ kuṇḍaṃ vāsiṣṭhaṃ putrajanmadam ..
yatra snātā ṛtau nārī sadyo garbhavatī bhavet ..
amogharetāḥ kāṃtā ca snānādatra prajāyate .. 24 ..

Moreover, here is an auspicious pond sacred to Vasiṣṭha, which grants the birth of sons, / where a woman having bathed during her season immediately becomes pregnant; / and the beloved woman's conception becomes unfailing by bathing here.