Because of Kṛṣṇa’s having sucked the breast of the Rākṣasī Pūtanā, when Kṛṣṇa killed her she was immediately freed of all material contamination. Her sinful reactions automatically vanished, and therefore when her gigantic body was being burnt, the smoke emanating from her body was fragrant like aguru incense.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
दह्यमानस्य देहस्य धूमश्चागुरुसौरभः । उत्थितः कृष्णनिर्भुक्तसपद्याहतपाप्मनः
dahyamānasya dehasya dhūmaścāgurusaurabhaḥ | utthitaḥ kṛṣṇanirbhuktasapadyāhatapāpmanaḥ
SB 10.6.34