Your spot on Chambo, here is the wikipedia extract. Happened on May 25 1991. A flight from Ethiopia to Tel Aviv. All the cargo holds would of been full to get them in for that number.
The operation set a world record for most passengers on an aircraft when an
El Al747 carried well over 1,000 people to Israel. The record itself is uncontested, but the number of passengers is unclear: Guinness World Records put the number at 1,088, including two babies who were born on the flight. It noted that contemporary reports cite numbers as low as 1,078 and as high as 1,122.