Jaiminīya (Talavakāra) Brāhmaṇa 2-7.216

Now, the five [and] twenty-fifth, that is this upward direction. The directions indeed milk heaven, or heaven milks the directions. He indeed obtains the milk of the directions and of heaven who knows thus. He who should desire: 'May I thrive with equal prosperity by an equal sacrifice; may I be firmly established; may I win the endless heavenly world'—he should sacrifice with these. He should choose a large sacrificial ground. Then he should tell [them] to construct five sheds: one here, one here, one here, one here, and one in the middle. With this [first one] he should sacrifice with the Rathantara-sāman. He thrives with this very prosperity, [reaches] this firm foundation, and wins this endless heavenly world. Then with this [second one] he should sacrifice with the Bṛhat-sāman; then with this [third one] he should sacrifice with the Rathantara-sāman; then with this [fourth one] he should sacrifice with the Bṛhat-sāman; then with this [central one] he should sacrifice with both sāmans. He thrives with this very prosperity, [reaches] this firm foundation, wins this endless heavenly world, and merges into this very direction. He becomes one of the directions; he merges into the directions. For him, this endless heavenly world is won. What belongs to these directions—the sāmans among them that have directions for finales and those that have viṣ for finales—they arrange them as leading to heaven, for the attainment of the heavenly world and for the prosperity of the forms of day and night.

Now these are the Ṛṣi-stomas.

The ṛṣis indeed won the heavenly world through toil, through austerity, [and] through the observance of vows.

They desired: 'Having established offspring in this world, let us go to the heavenly world.'