Because of mother Yaśodā’s hard labor, her whole body became covered with perspiration, and the flowers and comb were falling from her hair. When child Kṛṣṇa saw His mother thus fatigued, He became merciful to her and agreed to be bound.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स्वमातुः स्विन्नगात्राया विस्रस्तकबरस्रजः । दृष्ट्वा परिश्रमं कृष्णः कृपयाऽऽसीत्स्वबन्धने
svamātuḥ svinnagātrāyā visrastakabarasrajaḥ | dṛṣṭvā pariśramaṃ kṛṣṇaḥ kṛpayā''sītsvabandhane
SB 10.9.18