Srimad Bhagavatam Canto 11, Chapter 28, Text 18

SB 11.28.18

jñanam viveko nigamas tapas ca
 pratyaksam aitihyam athanumanam
ady-antayor asya yad eva kevalam
 kalas ca hetus ca tad eva madhye
 
Translation: 
 
Real spiritual knowledge is based on the discrimination of spirit from matter, and it is cultivated by scriptural evidence, austerity, direct perception, reception of the Puranas’ historical narrations, and logical inference. The Absolute Truth, which alone was present before the creation of the universe and which alone will remain after its destruction, is also the time factor and the ultimate cause. Even in the middle stage of this creation’s existence, the Absolute Truth alone is the actual reality.
 
Purport: 
 
Material scientists and philosophers are desperately searching for the ultimate material cause or principle, which is described here as kala, the time factor. The material process of cause and effect takes place entirely within a sequence of time; in other words, the time factor is the motivating impetus for material cause and effect. This time factor is a manifestation of the Supersoul, the form of the Supreme Lord that pervades and supports the cosmic manifestation. The method for acquiring knowledge is scientifically described here, and those who are serious, reasonable scholars will take advantage of the transcendental epistemology revealed here by the Lord.
Srimad Bhagavatam Canto 11, Chapter 28, Text 17
Srimad Bhagavatam Canto 11, Chapter 28, Text 19