According to our friend here, Malays were never Hindu. Sanskrit influenced the language, but Hinduism (in this case including Buddhism) never influenced the culture. Well he asked for a challenge so here you go
Evidence of the Hindu-Buddhist Malay heritage can be found in almost every aspect of the culture today. But let's start with something tangible. Here's an ancient statue of Avalokiteswara from Perak 
This inscription from Kedah is a Buddhist incantation. The religious belief of the Malays that carved this is not in doubt. This is not hanya sangkaan semata
Mak yong (yes that's how it's spelled, not "makyung") is among our oldest and most characteristically Malay performing art. While the dance itself is not Indian-influenced, many of the stories are of Hindu-Buddhist origin
Among the most prominent stories of wayang kulit are those based on Indian epics. Historically the most popular was the Ramayana. This is the reason both mak yong and wayang kulit are hated by Pas
One of the oldest styles of silat in Malaysia is Gayong Seri Rama, dating back to ancient Kedah. It was said to have been inspired by the movements of Rama, which is why the name was changed to "Pancasila Gayong Harimau" in recent decades
Evidence of pre-Islamic beliefs are especially common in Malay metaphysics, geomancy, mythology, and folklore. In some cases they were adapted after the conversion to Islam, but other times they remained unchanged
Examples of this can be seen in charms addressing Betara Guru (Shiva), Bisnu (Vishnu), Buda (Buddha) and many others. In fact it was believed the steel used for forging the very Malay keris came from the Hindu gods
Asking if Malays were ever Hindu is like asking if Greeks ever worshipped Zeus. There's far too much evidence to even try to fit in a Twitter thread. But for a start, I recommend picking up this book
