AYYAMU’L-BIZ أيام ألبس
“The days of the bright nights’.” mentioned in the Miskat (book vii. c.7, part 3). as days one which Muhammad did not eat, whether halting or marching. They are the 13th, 14th, and 15th nights of the month. (See Lane’s Dict., p. 284).
Based on Hughes, Dictionary of Islam