Dusky Warbler

The dusky warbler is small with buff underparts, a whitish supercilium and a brown back. It has an orangish-yellow bill. 

Illustration of dusky warbler from Birds of the World. 

It winters in South and Southeast Asia and breeds in Siberia, Mongolia and China.

Range of dusky warbler from Birds of the World.

Oddly enough, the only place I saw it was at our hotel in Guwahati, Assam, India, in a fountain.