Option 1: Vinaya Pitaka is one of the three divisions of the Buddhist scriptures. It primarily deals with rules and regulations for monastic discipline. While it contains valuable information about the monastic community, it does not specifically mention the Mauryan Emperor Ashoka.

Option 2: Sutta Pitaka is another division of the Buddhist scriptures. It consists of discourses attributed to the Buddha and his teachings. While it contains a wealth of spiritual teachings, it does not explicitly mention Ashoka or his account.

Option 3: Abhidhamma Pitaka is the third division of the Buddhist scriptures and focuses on the analysis and interpretation of the Buddha`s teachings. Similar to the other options, it does not contain an account of Emperor Ashoka.

Option 4: Mahavamsa is a chronicle written in the Pali language that provides a historical account of Sri Lanka. It is considered one of the most important sources of information about the early history of Buddhism in Sri Lanka. The Mahavamsa includes an account of Emperor Ashoka`s interactions with Buddhism and his role in promoting the religion. Therefore, option 4 is the correct answer.