Garudapurana 2.34.20

2.34.20

śūdro gacchati sarvatra vaiśyastriṣu dvayoḥ paraḥ /
gacchati svīyavarṇeṣu dātuṃ prete jalāñjalim //

A Śūdra goes everywhere; a Vaiśya among three; the next [a Kṣatriya] among two; / [a Brahmin] goes among his own castes to offer a handful of water to a deceased spirit.