The incident relating to King Chakrawati Farmas is documented in an old manuscript in the India Office Library, London, which has reference number: Arabic, 2807, 152-173. It is quoted in the book “Muhammad Rasulullah,” by M. Hamidullah:
“There is a very old tradition in Malabar, South-West Coast of India, that Chakrawati Farmas, one of their kings, had observed the splitting of the moon, the celebrated miracle of the Holy Prophet (pbuh) at Mecca, and learning on inquiry that there was a prediction of the coming of a Messenger of God from Arabia, he appointed his son as regent and set out to meet him. He embraced Islam at the hand of the Prophet, and when returning home, at the direction of the Prophet, died at the port of Zafar, Yemen, where the tomb of the “Indian king” was piously visited for many centuries.”
The old manuscript in the 'India Office Library' contains several other details about King Chakrawati Farmas and his travel...
According to Maududi, the traditionists and commentators have agreed that this incident took place at Mina in Makkah about five years before the Holy Prophet's Hijra (migration) to Madinah...
It is due to this incident about their king, the people of Malabar became the first community in India to accept Islam. Subsequently, they increased their trade with Arabs, as the Arab ships used to pass by their shores on the way to China before the advent of Prophet Muhammad (pbuh).
Before Prophet Muhammad (pbuh), Malabar also had a Christian community dating back from the earliest followers of Prophet Jesus ('Isa), pbuh. St. Thomas is believed to have migrated to India and died there. This community remained untouched by later theological developments in Christianity until the arrival of Portugese traveler Vasco da Gama.
When the British were consolidating their stronghold in India, they deployed the largest naval operation (on the shores of India) against the Muslims of Malabar.