Trade between the Arabian Peninsula and South East Asia (SEA) is older than the history of Islam. Arabs were not foreign to SEA when Islam started to emerge. The Maritime trade played a very important role for Islam to spread in SEA, especially Indonesian Archipelago.

Actually the arrival of Islam in Malaysia happened a lot later than the Indonesian Archipelago. Although on the mainland SEA Muslim Arabs were active, the actual mass Islamisation finds its way from India to today's Malaysia around 11th century.

If you are interested look into the following reading materials:

Chaudhuri, K.N. (1990): Asia before Europe: Economy and Civilisation of the Indian Ocean from the Rise of Islam to 1750, Cambridge et al.

Wink, André (1990): Al-Hind: The Making of the Indo-Islamic World, Vol. 1: Early Medieval India and the Expansion of Islam, Leiden: Brill.

Merchantmen in the Western Seaboard of India: A Maritime Profile (500 BCE-1500 CE)”, in: Prakash: Trading World of the Indian Ocean

Fernando, M. R.: “Commerce in the Malay Archipelago”, in: Prakash (ed.): Trading World of the Indian Ocean

I have a lot more sources. If you are interested send me a pm and I will let you know about them.