This is the plain Prinia. Often glimpsed, but surprisingly hard to get a good photo with a nice background, but my patience paid off.
The plain prinia (Prinia inornata), is also known as the plain wren-warbler or white-browed wren-warbler.
It is a small cisticolid warbler found in southeast Asia. The family Cisticolidae is a group of about 160 warblers, small passerine birds found mainly in warmer southern regions of the Old World.