Srimad-Bhagavatam: Canto 6 - Chapter 1 - Verse 4-5
एकदा स विमानेन विष्णुदत्तेन भास्वता ।गिरिशं ददृशे गच्छन् परीतं सिद्धचारणै: ॥ ४ ॥आलिङ्गयाङ्कीकृतां देवीं बाहुना मुनिसंसदि ।उवाच देव्या: शृण्वन्त्या जहासोच्चैस्तदन्तिके ॥ ५ ॥
ekadā sa vimānenaviṣṇu-dattena bhāsvatāgiriśaṁ dadṛśe gacchanparītaṁ siddha-cāraṇaiḥ
One time while King Citraketu was traveling in outer space on a brilliantly effulgent airplane given to him by Lord Viṣṇu, he saw Lord Śiva, surrounded by Siddhas and Cāraṇas. Lord Śiva was sitting in an assembly of great saintly persons and embracing Pārvatī on his lap with his arm. Citraketu laughed loudly and spoke, within the hearing of Pārvatī.
Śrīla Viśvanātha Cakravartī Ṭhākura says in this connection, The purport is that the Supreme Personality of Godhead wanted to bring Citraketu to Vaikuṇṭhaloka as soon as possible. The Lord’s plan was that Citraketu be cursed by Pārvatī to become Vṛtrāsura so that in his next life he could quickly return home, back to Godhead. There have been many instances in which a devotee acting as a demon has been brought to the kingdom of God by the mercy of the Lord. For Pārvatī to be embraced by Lord Śiva was natural in a relationship between husband and wife; this was nothing extraordinary for Citraketu to see. Nonetheless, Citraketu laughed loudly to see Lord Śiva in that situation, even though he should not have done so. Thus he was eventually cursed, and this curse was the cause of his returning home, back to Godhead.