Ansonia minuta Dwarf Slender Toad
Some other names for this species:
Minute Slender Toad
Kubah National Park, Sarawak, MalaysiaJanuary 27, 2017
Dwarf Slender Toad (Ansonia minuta)
Frogs of Borneo assures me that this is a common lowland stream toad, though I saw only one in two nights full of frogs at Kubah National Park. A fully grown specimen is about an inch long.

My Travelogues and Trip Lists page includes a complete list of the herps I saw in the wild on this trip to Malaysia, as well as a travelogue of the trip.

Kubah National Park, Sarawak, MalaysiaFebruary 18, 2018
Dwarf Slender Toad (Ansonia minuta)
I saw one more in the same area at Kubah the next year, so maybe that's enough to call them common?
Online references:
Printed references: