What is the ruling on someone to whom another said, "Have you memorized such-and-such a Surah?" and he replied with "Yes" when he had not memorized it, then regretted his statement?

You must initiate sincere repentance to Allah Almighty and resolve never to return to lying, for it is forbidden. This is based on the Prophet's (peace be upon him) saying: "You must adhere to truthfulness, for truthfulness leads to righteousness, and righteousness leads to Paradise. A man continues to be truthful until he is recorded as a truthful person with Allah. And beware of lying, for lying leads to wickedness, and a man continues to lie until he is recorded as a liar with Allah."