Purāṇas · Viṣṇu/Vāyu/Matsya/Brahmāṇḍa c. 3rd-5th c. CE; Bhāgavata c. 9th-10th c. CE
पुच्छेग्निश्च महेन्द्र श्च कश्यपोथ ततो ध्रुवः । तारका शिशुमारस्य नास्तमेति चतुष्टयम् ॥ ३४ ॥
Agni, Mahendra, Kaśyapa, and Dhruva, in succession, are placed in its tail; which four stars in this constellation never set. — H.H. Wilson (1840; public domain)
One of the most stable elements in the whole tradition: Indra appears in the tail-group in every recension (Bhāgavata 5.23.1 and 5.23.5; Viṣṇu P. 2.12.34 and Vāyu/Matsya/Brahmāṇḍa as Mahendra), and Viṣṇu P. 2.12.34 explicitly states that the four tail-figures are stars that NEVER SET — i.e. circumpolar. That is a real, falsifiable astronomical claim in the text. Which visible star is meant is nowhere stated; proposals that make Indra a former pole star are modern reconstruction.
Viṣṇu Purāṇa 2.12.34; Bhāgavata Purāṇa 5.23.5 (and 5.23.1); Vāyu Purāṇa 52.95; Matsya Purāṇa 127.25; Brahmāṇḍa Purāṇa 1,23.104 · text · translation