Khandogya-Upanishad: Fourth Prapathaka, Fifth Khanda

1. The bull of the herd (meant for Vayu) said to him: “Satyakama!” He replied: “Sir!” The bull said: “We have become a thousand, lead us to the house of the teacher;

2. “And I will declare to you one foot of Brahman.”

“Declare it, Sir,” he replied.

He said to him: “The eastern region is one quarter, the western region is one quarter, the southern region is one quarter, the northern region is one quarter. This is a foot of Brahman, consisting of the four quarters, and called Prakasavat (endowed with splendour).

3. “He who knows this and meditates on the foot of Brahman, consisting of four quarters, by the name of Prakasavat, becomes endowed with splendour in this world. He conquers the resplendent worlds, whoever knows this and meditates on the foot of Brahman, consisting of the four quarters, by the name of Prakasavat.