Garudapurana 2.26.25

2.26.25

jyeṣṭhasyaiva kaniṣṭhena bhrātṛputtreṇa bhāryayā /
sapiṇḍīkaraṇaṃ kāryaṃ putrahīne nare khaga //

For a childless man, O Bird, the sapiṇḍīkaraṇa rite / must be performed by a younger brother, a brother's son, or the wife.