What is the ruling on one who doubts the number of expiations (kaffarat) due upon him—whether they are four, five, or six—after he swore to abandon a specific action and then returned to it multiple times?

Whoever doubts the number of expiations (kaffarat) required of him, then the minimum certain amount is obligatory upon him, because the default is the exoneration of one's responsibility, as mentioned by Shaykh Abu Muhammad bin Abd al-Salam. For Allah created His servants with their responsibilities exonerated until the causes of obligation are realized.