Markandeyapurana 35.49

35.49

jāte putre pituḥ strānaṃ sacelantu vidhīyate /
tatrāpi yadi cānyasmin jāte jāyeta cāparaḥ //

This same ordinance is applied also to the impurity caused by the birth of sapiṇḍas, among sapiṇḍas and properly among sahodakas also. When a son is born, the father must bathe with his clothes on. And if, after one child has been born there, another should be born, the purification in that case also is prescribed according to the days of the elder-born child.