SB 12.2.30

yāvat sa pāda-padmābhyāṁ
 spṛśan āste ramā-patiḥ
tāvat kalir vai pṛthivīṁ
 parākrantuṁ na cāśakat
Word for word: 
yāvat — as long as; saḥ — He, Lord Śrī Kṛṣṇa; pāda-padmābhyām — with His lotus feet; spṛśan — touching; āste — remained; ramā-patiḥ — the husband of the goddess of fortune; tāvat — for that long; kaliḥ — the Age of Kali; vai — indeed; pṛthivīm — the earth; parākrantum — to overcome; na — not; ca — and; aśakat — was able.
Translation: 
As long as Lord Śrī Kṛṣṇa, the husband of the goddess of fortune, touched the earth with His lotus feet, Kali was powerless to subdue this planet.
Purport: 

Although even during the time of Lord Kṛṣṇa’s presence on earth Kali had entered the earth to a slight extent through the impious activities of Duryodhana and his allies, Lord Kṛṣṇa consistently suppressed Kali’s influence. Kali could not flourish until Lord Kṛṣṇa had left the earth.