Is it necessary to repeat ablution and prayer if one expels gas after ablution due to obsessive-compulsive disorder (OCD) which causes a long time to be spent in preparation for prayer, and what about past prayers?

"Wasaaws" (obsessive whisperings/thoughts) are among the most evil ailments. It is incumbent upon the one afflicted by them to seek treatment by relying on Allah, then on trustworthy doctors. They must also strive against their own self. The most beneficial cure for "wasaaws" after supplication is complete disregard for them. Our advice to you is not to stay in the restroom for an excessive period. Once you exit, perform ablution and then pray without paying attention to the "wasaaws." Re-performing ablution is not obligatory unless there is absolute certainty of passing wind afterwards (a certainty one could swear upon). Past prayers are valid as long as there was no absolute certainty of invalidating one's ablution after performing it; this is because it appears that all of this is due to the symptoms of "wasaaws."