In Brahma Vaivarta Puraana , Prakriti Khanda , Chapter 58
After stealing Taaraa wife of Brihaspati, Chandra went to refuge of Shukra Deva the Guru of Asuras.
बभूव शरणापन्नो भीतो दैत्येषु चन्द्रमाः ।
तेजस्विनि तथा शुक्रे तेषां च बलिनां गुरौ ॥ ४० ॥
अभयं च ददौ तस्मै कृपया भृगुनन्दनः ।
गुरुं जहास देवानां सुविपक्षं बृहस्पतिम् ॥ ४१ ॥
सभायां जहसुर्हृष्टा बलिनो दितिनन्दनाः ।
अभयं च ददुस्तस्मै भीताय च कलङ्किने ॥ ४२ ॥
सतीसतीत्वध्वंसेन पापिष्ठचन्द्रमण्डले ।
बभूव शशरूपं च कलंकं निर्मले मलम् ॥ ४३ ॥
The frightened Chandramaa got refuge in the Daityas and the resplendent Shukra Deva who is Guru of those powerful Daityas. 40.
Shukra the son of Bhrigu, out of his mercy told Chandra "Do not fear" ,
and laughed at the Guru of Devas, Brihaspati, who is the fast opposition of Shukra. 41 .
Then all the Daityas, sons of Diti who are valourous and powerful also laughed in that court,
and told Chandra not to fear, who was frightened as well as defamed. 42 .
Due to destroying the purity of pious lady (Taaraa) an impure spot mark in Shape of Rabbit came on the pure Sphere of Moon who had committed a sin. 43 .
This is the reason we see a vague Rabbit mark on Moon Sphere (Chandra Mandala).