Skandapurana 5.202.16

5.202.16

api cāṣṭakulotpannaḥ sāmānyaḥ kiṃ punarhi yaḥ..
aśuddhena tu vipreṇa yaḥ śrāddhā dyaṃ karoti hi ..
tasya bhasmahutaṃ yadvatsarvaṃ tajjāyate vṛthā ..16..

Even one born in the eight families, how much more so an ordinary one! / Indeed, for one who performs śrāddha and the like with an unpurified brahmin, / all of that becomes futile, like an oblation poured into ashes. // 16