SB 5.17.21

yam āhur asya sthiti-janma-saṁyamaṁ
 tribhir vihīnaṁ yam anantam ṛṣayaḥ
na veda siddhārtham iva kvacit sthitaṁ
 bhū-maṇḍalaṁ mūrdha-sahasra-dhāmasu
Synonyms: 
yam — whom; āhuḥ — they said; asya — of the material world; sthiti — the maintenance; janma — creation; saṁyamam — annihilation; tribhiḥ — these three; vihīnam — without; yam — which; anantam — unlimited; ṛṣayaḥ — all the great sages; na — not; veda — feels; siddha-artham — a mustard seed; iva — like; kvacit — where; sthitam — situated; bhū-maṇḍalam — the universe; mūrdha-sahasra-dhāmasu — on the hundreds and thousands of hoods of the Lord.
Translation: 
Lord Śiva 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 Śeṣa 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: 

The incarnation of the Supreme Personality of Godhead known as Śeṣa 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 Śrī Caitanya-caritāmṛta, Ādi-līlā, Chapter Five, verses 117-125. There it is stated that Lord Viṣṇu’s incarnation as the serpentine Ananta Śeṣa Nāga 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.