I don't have access to my bird books, but it looks very cisticola-ish, however I don't remember any species with a clean breast and belly. If not a cisticola then most likely a warbler.
the light is washing out all the back of the bird, but maybe Cisticola cantans. I think the crown and wings look rufous, and the undertail looks right.
I have just found some pictures of a different individual but the same species (which was quite common around Nairobi National Park) which shows the back well.
I think the rufous colouring on the sides of the wings show that it's a Winding Cisticola C. galactotes?
