Can I visit Singapore from Malaysia and come back soon during my travel itinerary?

I'm in Kuala Lumpur right now, and have a ticket to go to Ho Chi Minh.

However, I consider visiting Singapore for a few days and then come back to KL. I consider a bus trip.

But I'm fearful of being denied of the re-entry when I come back from Singapore due to the short interval. That would invalidate my travel to HCMC, and I would have to buy a new ticket from Singapore for another place (except Malaysia).

Is it possible to make a short trip to Singapore from Malaysia and then come back?