The Lord lay down for a thousand cycles of four yugas in His internal potency, and by His external energy He appeared to be sleeping within the water. When the living entities were coming out for further development of their fruitive activities, actuated by the energy called kāla-śakti, He saw His transcendental body as bluish.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
चतुर्युगानां च सहस्रमप्सु स्वपन् स्वयोदीरितया स्वशक्त्या । कालाख्ययाऽऽसादितकर्मतन्त्रो लोकानपीतान् ददृशे स्वदेहे
caturyugānāṃ ca sahasramapsu svapan svayodīritayā svaśaktyā | kālākhyayā''sāditakarmatantro lokānapītān dadṛśe svadehe
SB 3.8.12