Srimad Bhagavatam Canto 03, Chapter 15, Text 15

SB 3.15.15

yatra cadyah puman aste
 bhagavan sabda-gocarah
sattvam vistabhya virajam
 svanam no mrdayan vrsah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
In the Vaikuntha planets is the Supreme Personality of Godhead, who is the original person and who can be understood through the Vedic literature. He is full of the uncontaminated mode of goodness, with no place for passion or ignorance. He contributes religious progress for the devotees.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The kingdom of the Supreme Personality of Godhead in the spiritual sky cannot be understood by any process other than hearing from the description of the Vedas. No one can go see it. In this material world also, one who is unable to pay to go to a far distant place by motorized conveyances can only understand about that place from authentic books. Similarly, the Vaikuntha planets in the spiritual sky are beyond this material sky. The modern scientists who are trying to travel in space are having difficulty going even to the nearest planet, the moon, to say nothing of the highest planets within the universe. There is no possibility that they can go beyond the material sky, enter the spiritual sky and see for themselves the spiritual planets, Vaikuntha. Therefore, the kingdom of God in the spiritual sky can be understood only through the authentic descriptions of the Vedas and Puranas.
In the material world there are three modes of material qualities — goodness, passion and ignorance — but in the spiritual world there is no trace of the modes of passion and ignorance; there is only the mode of goodness, which is uncontaminated by any tinge of ignorance or passion. In the material world, even if a person is completely in goodness, he is sometimes subject to be polluted by tinges of the modes of ignorance and passion. But in the Vaikuntha world, the spiritual sky, only the mode of goodness in its pure form exists. The Lord and His devotees reside in the Vaikuntha planets, and they are of the same transcendental quality, namely suddha-sattva, the mode of pure goodness. The Vaikuntha planets are very dear to the Vaisnavas, and for the progressive march of the Vaisnavas toward the kingdom of God, the Lord Himself helps His devotees.
Srimad Bhagavatam Canto 03, Chapter 15, Text 14
Srimad Bhagavatam Canto 03, Chapter 15, Text 16