Verse 63

अथैतस्मिन्महालोके तिष्ठन्नुद्दालकश्चिरम् ।अपश्यद्व्योमगान्सिद्धानमरानपि भूरिशः

In plain words

Then, remaining long in this great light, Uddālaka saw siddhas moving through the sky, and immortals too, in great numbers.