The claim that price discrimination yields higher profits than a single-price strategy for a monopolist is a fundamental microeconomic principle (derived from standard monopoly pricing theory), and no citation is needed.
The claim represents a standard textbook economic truism about monopoly behavior and profit maximization under different forms of price discrimination (first, second, or third degree). Per instructions, trivially true economic or mathematical definitions of this nature are classified as common knowledge and require no citation of empirical papers.