Is it permissible for someone who has committed a sin requiring a Hadd punishment or an oath to lie before the ruler to save himself from death, on the principle of committing the lesser of two harms and averting the greater corruption?

Lying is not legislated in the oaths of li'an (oath of condemnation), due to the involvement of others' rights and the descent of curse and wrath upon the liar. The Prophet, peace and blessings be upon him, emphasized the gravity to those performing li'an and warned them against the consequences of lying.

As for the hudud (prescribed punishments) of Allah Almighty, such as fornication and drinking alcohol, if a person confesses to them and then retracts their confession, the hadd is dropped. It is recommended for the sinner to conceal themselves and not confess. If asked about an abomination committed between them and Allah, they may deny it verbally, even if they are lying, to preserve their life, property, and honor. This is based on the Prophet's, peace and blessings be upon him, saying: "Whoever commits any of these abominations should conceal themselves with the concealment of Allah."