स होवाच विजानाम्यहं यत्प्राणो ब्रह्म कं च तु खं च न विजानामीति ते होचुर्यद्वाव कं तदेव खं यदेव खं तदेव कमिति प्राणं च हास्मै तदाकाशं चोचुः ॥ ४.१०.५ ॥
In plain words
He said, "I understand that the breath is Brahman; but joy and space I do not understand." They said, "What is joy, that is space; and what is space, that is joy." And they told him of the breath and of that space.