In order to answer this, one must distinguish between the formal SILL 
diagram of Hicksian vintage, the equations of Harrod, and those of Meade, 
the IS-LM of Hansen, and IS-LM as a conceptual framework for economic 
analysis.

In the latter case, James Meade's "An Introduction to Economic Analysis and 
Policy" (1936, 2nd ed. 1937) and the US edition by Meade, edited by Hitch, 
with an introduction by Hansen (1938), represent, in my view at least, the 
"first undergraduate macroeconomics textbook" based upon the IS-LM 
conceptual framework...

A discussion of these works can be found in Young (1987, 1989)...

Warren Young