The most convenient source of information on homogeneous functions is <A HREF="https://en.wikipedia.org/wiki/Homogeneous_function">Wikipedia</A>; if that is not satisfactory as a source, you could cite: 

J.P. Lewis, <A HREF="https://doi.org/10.1007/978-1-349-15324-4_22">Homogeneous Functions and Euler’s Theorem.</A> In: *An Introduction to Mathematics* (Palgrave Macmillan, London, 1969).