Skandapurana 16.208.45

16.208.45

pramātāmahastu hṛdaye vṛddho nābhau tu saṃsthitaḥ ..
alābhe brāhmaṇasyaiva kuśaḥ kāryo dvijaḥ priye ..
idaṃ sarvapurāṇebhyaḥ sāramuddhatya cocyate .. 45 ..

The maternal great-grandfather is in the heart, and the elder is established in the navel. / In the absence of a brahmin, dear lady, a brahmin should be made of kuśa grass. / This is declared having extracted the essence from all the Purāṇas. (45)