SB 5.17.21
yam ahur asya sthiti-janma-samyamam
tribhir vihinam yam anantam rsayah
na veda siddhartham iva kvacit sthitam
bhu-mandalam murdha-sahasra-dhamasu
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Lord Siva continued: All the great sages accept the Lord as the source of creation, maintenance and destruction, although He actually has nothing to do with these activities. Therefore the Lord is called unlimited. Although the Lord in His incarnation as Sesa holds all the universes on His hoods, each universe feels no heavier than a mustard seed to Him. Therefore, what person desiring perfection will not worship the Lord?
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The incarnation of the Supreme Personality of Godhead known as Sesa or Ananta has unlimited strength, fame, wealth, knowledge, beauty and renunciation. As described in this verse, Ananta’s strength is so great that the innumerable universes rest on His hoods. He has the bodily features of a snake with thousands of hoods, and since His strength is unlimited, all the universes resting on His hoods feel no heavier than mustard seeds. We can just imagine how insignificant a mustard seed is on the hood of a serpent. In this connection, the reader is referred to Sri Caitanya-caritamrta, Adi-lila, Chapter Five, verses 117-125. There it is stated that Lord Visnu’s incarnation as the serpentine Ananta Sesa Naga supports all the universes on His hoods. By our calculation, a universe may be very, very heavy, but because the Lord is ananta (unlimited), He feels the weight to be no heavier than a mustard seed.