Matsya Purana 273.60

273.60

kṣīṇe kaliyugecaiva tiṣṭhantīti kṛte yuge.
saptarṣayastu taiḥ sārdhaṃ madhye tretāyuge punaḥ .. 273.59

Even after the close of the Kali Yuga the Seven Sages who continue to exist along with these two throughout the Kṛita Yuga will then incarnate in the middle of the (future) Tretâ Yuga. They will take birth in order to be the seeds of Brâhmanas and Kṣatriyas (of Brahmanic parentage) again. Thus at the end of the Puṣya asterism (when the Great Bear is in a line with that asterism) the Seven Sages, along with those kings (take birth on earth) for the sake of procreating offsprings in every Yuga. Thus the Brâhmanas know the close relationship of the Kṣatriyas with the Brâhmanas (and how several Kṣatriya dynasties had Brâhmaṇa paternity).—62