Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 10

Sanskrit:

भूतसूक्ष्मात्मनि मयि तन्मात्रं धारयेन्मन: ।अणिमानमवाप्नोति तन्मात्रोपासको मम ॥ १० ॥

ITRANS:

bhūta-sūkṣmātmani mayitan-mātraṁ dhārayen manaḥaṇimānam avāpnotitan-mātropāsako mama

Translation:

One who worships Me in My atomic form pervading all subtle elements, fixing his mind on that alone, obtains the mystic perfection called aṇimā.

Purport:

Aṇimā refers to the mystic ability to make oneself smaller than the smallest and thus able to enter within anything. The Supreme Personality of Godhead is within the atoms and atomic particles, and one who perfectly fixes his mind in that subtle atomic form of the Lord acquires the mystic potency called aṇimā, by which one can enter within even the most dense matter such as stone.