One of the primary sources for Ricardo’s ideas on the labour theory of value is his seminal work:

• Ricardo, David. (1817). On the Principles of Political Economy and Taxation.
 This work lays out Ricardo’s perspective on value, where he examines how the labour embodied in commodities, along with other factors such as wages and profits, contributes to their value.

Additional scholarly works analyzing Ricardo’s theory include:

• Heffron, W. (1988). Ricardo’s Theory of Value. In A. O. Lindsey (Ed.), Readings in the History of Economic Thought.
 This collection offers commentary and analysis on Ricardo’s methodology and provides context for his labour-based approach to value.

• Sraffa, P. (1960). Production of Commodities by Means of Commodities.
 Although primarily concerned with price determination in a system influenced by classical ideas, Sraffa engages with Ricardo’s value principles, offering insights into how labour inputs factor into the theory.

These references provide a basis for understanding how Ricardo’s work contributes to the development of the labour theory of value. If you require further in-depth exploration, consulting annotated editions of Ricardo’s writings or comprehensive histories of economic thought will be beneficial.