You (Devaki and Vasudeva) spent twelve thousand celestial years performing difficult activities of tapasya in consciousness of Me (Krsna consciousness) - SB 10.3.36

Expressions researched:
"Thus you spent twelve thousand celestial years performing difficult activities of tapasya in consciousness of Me" |"Kṛṣṇa consciousness"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

Thus you spent twelve thousand celestial years performing difficult activities of tapasya in consciousness of Me [Kṛṣṇa consciousness].

SB 10.3.36, Translation

Thus you spent twelve thousand celestial years performing difficult activities of tapasya in consciousness of Me [Kṛṣṇa consciousness].