Does expiation become obligatory for doubt concerning matters of prayer, for repeated oaths uttered in a moment of anger, for an oath sworn with a forgotten wording, and for an oath in which lying is probable?

Doubts related to obsessive thoughts should be ignored. Some of the mentioned instances are not oaths to begin with, such as the second and third scenarios. If an oath was uttered unintentionally, it is considered a 'laghw' (idle talk) for which no expiation is required, like the fourth and perhaps the first scenario. For an oath concerning a past event, the majority of scholars hold that no expiation is required, and repentance is necessary only if one intentionally lied. As for an oath intended by the heart, expiation becomes obligatory if one breaks it. If there is doubt about the validity of an oath, the default is that it is not valid, and nothing is required. However, if you are certain of its validity, expiation is obligatory for each oath broken. According to the Hanbalis, a single expiation suffices to alleviate hardship.