In Perak, it was the custom in ancient times to perform periodically (once in seven years or once in every Raja’s reign) a ceremony intended to ensure the prosperity of the state by the propitiation of friendly spirits and the expulsion of evil influences. This was spoken of as pelas negeri, the cleansing of the country from evil (menchuchikan negeri dari segala bahaya).
The ceremony has been described to me as follows: The Raja, chiefs and a great following of people assembled at a selected spot, as far up the river as possible, short of the rapids which impede navigation. Jeram Kerenga was the usual place of meeting. There a number of bamboo rafts, some of them of elaborate construction with houses on them (balai gambang) were made. The four principal rafts were devoted to the propitiation of the four great classes of spirits in perak, namely the Hantu Blian, or tiger spirits, the Hantu Sungkei, the Hantu Malayu and the Jin Raja. In each a number of pawangs (medicine man) took up their station according to the particular class of demons which they affected. The first raft was the one prepared for the Hantu Blian and on it a Prah tree, felled for the purpose, was placed erect with all its branches complete. It was kept in a position by stays (tambirang).
When all were ready, the procession of rafts started down the river, those of the Hantu’s leading the way. Behind them came a raft containing persons engaged in religious exercises (mengaji). Then came a raft with the Nobat (royal band) and then the Raja, chiefs and people in rafts of various sorts. As they floated down the river with the stream, the chief pawangs in the leading rafts waved (melambai) white clothes and shouted invocations to the spirits and demons inhabiting the state through which they were passing, inviting them to come on board the rafts and eat what was provided for them. While thus engaged, the chief pawing in each of the four spirits rafts stood upon a slab of tin, which was his perquisite.
A halt was made at every kampong on the river banks of sufficient importance to have a mosque, and at each a buffalo, subscribed for by the people (meripai), was slaughtered and the head placed on one of the spirit-rafts. The rest was eaten by the people. The ceremony ended at Bras basah, a kampong on the left bank of the Perak river not far from its mouth, where the rafts were abandoned and allowed to drift out to sea.
Maxwell, W. Notes and Queries 3. In W. Maxwell, Notes and Queries of the Malaysian Branch Royal Asiatic Society (reprint 15). Kuala Lumpur: Malaysian Branch Royal of the Royal Asiatic Society; 1997. p93-94.