Top sages on Wednesday led the mass worship at the Western Wall, chanting dirges of penitence for an impending pullout that Jewish extremists consider a betrayal of a biblical birthright and a reward for a 4 1/2-year-old Palestinian uprising.
"Just like in Sodom, the government has decided on an action that is inconsistent with morality," one rabbi said, referring to the Bible's account of a licentious town destroyed by God. The same incident is mentioned in the Quran.
Police sources said a crowd of 50,000 had come to the wall in Jerusalem's Old City, where Jews often gather to mourn the loss of ancient temples. Pro-settlement organisers put the number at twice as many.
Polls show that a majority of Israelis support quitting Gaza and a corner of the West Bank in what Prime Minister Ariel Sharon calls a bid to "disengage" from conflict with the Palestinians.
The plan was passed by parliament and the cabinet despite fierce political opposition, including from inside Sharon's party. The evacuations are scheduled to begin next week.
A rash of violent acts by anti-pullout activists - including the killing of four Israeli Arabs by a Jewish militant last week - have stoked government fears of strife during the pullout.
The umbrella Yesha settler council has called for resistance to the evacuations to be non-violent.
Palestinians welcome Israeli withdrawals from land occupied in the 1967 Israeli-Arab war, but suspect Sharon plans to give up Gaza while cementing a hold on major West Bank settlement blocs.