Harry Potter and the Half-Blood Prince
"My mother can't have been magic, or she wouldn't have died," said Riddle, more to himself than Dumbledore. (13.167)
"I went into the girl's bathroom just before I came in here and there were about a dozen girls in there, including Romilda Vane, trying to decide how to slip you a love potion." (15.13)
"The old argument," he said softly. "But nothing I have seen in the world has supported your pronouncements that love is more powerful than my kind of magic, Dumbledore."
"Perhaps you have been looking in the wrong places," suggested Dumbledore. (20.172-173)