What is the ruling on fasting Thursday, October 14, 2004, given that it was the completion of the month of Sha'ban, and the first day of Ramadan was supposed to be Friday, October 15, 2004?

Scholars have differed regarding fasting on the Day of Doubt (the 30th of Sha'ban, if the crescent of Ramadan is not sighted). Most of them hold that it is disliked to fast on this day if one does so believing it to be from Ramadan, citing the Hadith of Ammar bin Yasir: "Whoever fasts on the Day of Doubt has disobeyed Abu al-Qasim (peace be upon him)." If your colleague fasted it as a precaution for Ramadan, then he must seek forgiveness and not repeat such an act. However, if he fasted it voluntarily, or to make up for missed fasts, or as part of continuous fasting, or if it coincided with a vow, then there is no harm in that.