MUṆḌAKA UPANISHAD · 2.1.8

सप्त प्राणाः प्रभवन्ति तस्मात्सप्तार्चिषः समिधः सप्त होमाः ।
सप्त इमे लोका येषु चरन्ति प्राणा
गुहाशया निहिताः सप्त सप्त ॥ ८॥

sapta prāṇāḥ prabhavanti tasmātsaptārciṣaḥ samidhaḥ sapta homāḥ ।
sapta ime lokā yeṣu caranti prāṇā
guhāśayā nihitāḥ sapta sapta ॥ 8॥

The seven breaths are born from Him and the seven lights and kinds of fuel and the seven oblations and these seven worlds in which move the life-breaths set within with the secret heart for their dwelling-place, seven and seven.

Sri Aurobindo · CWSA 18, p. 138