One verse

Srimad Bhagavatam 11.21.9

11.21.9

कर्मण्यो गुणवान् कालो द्रव्यत: स्वत एव वा । यतो निवर्तते कर्म स दोषोऽकर्मक: स्मृत: ॥ ९ ॥

karmaṇyo guṇavān kālo dravyataḥ svata eva vā yato nivartate karma sa doṣo ’karmakaḥ smṛtaḥ

karmaṇyaḥ
suitable for executing one’s prescribed duty
guṇavān
pure
kālaḥ
time
dravyataḥ
by achievement of auspicious objects
svataḥ
by its own nature
eva
indeed
vā
or
yataḥ
due to which (time)
nivartate
is impeded
karma
one’s duty
saḥ
this (time)
doṣaḥ
impure
akarmakaḥ
inappropriate for working properly
smṛtaḥ
is considered

A specific time is considered pure when it is appropriate, either by its own nature or through achievement of suitable paraphernalia, for the performance of one’s prescribed duty. That time which impedes the performance of one’s duty is considered impure.