SB 11.7.49

kālena hy ogha-vegena
 bhūtānāṁ prabhavāpyayau
nityāv api na dṛśyete
 ātmano ’gner yathārciṣām
Synonyms: 
kālena — by time; hi — indeed; ogha — like a flood; vegena — whose speed; bhūtānām — of created bodies; prabhava — the birth; apyayau — and demise; nityau — constant; api — although; na dṛśyete — are not seen; ātmanaḥ — related to the spirit soul; agneḥ — of fire; yathā — just as; arciṣām — of the flames.
Translation: 
The flames of a fire appear and disappear at every moment, and yet this creation and destruction is not noticed by the ordinary observer. Similarly, the mighty waves of time flow constantly, like the powerful currents of a river, and imperceptibly cause the birth, growth and death of innumerable material bodies. And yet the soul, who is thus constantly forced to change his position, cannot perceive the actions of time.
Purport: 

The brāhmaṇa avadhūta instructing King Yadu again gives the example of fire after having already proceeded to the example of the moon. This analytic method is called siṁhāvalokana, or “the lion’s glance,” by which one simultaneously proceeds forward and casts backward glances to see if anything has been overlooked. Thus the sage proceeds with his analysis but returns to the example of fire to illustrate the need for renunciation. The material body is certainly an ephemeral and phantasmagorical manifestation of the Lord’s external potency. The flames of a fire constantly take birth and disappear, yet we perceive the fire as a continuous reality. Similarly, the soul is a continuous reality, although his material bodies appear and disappear constantly, by the influence of time. It is said that the most astonishing thing is that no one thinks that they will die. Because the soul is eternal, the living entity is prone to accept any fleeting situation as permanent, forgetting that his eternal nature can be truly experienced only in the eternal atmosphere of the spiritual sky. If one is convinced of this fact, he develops the quality of vairāgya, or detachment from material illusion.