Friday's massacre during prayers in the North Sinai town of Rawda killed at least 300 people when suspected IS gunmen surrounded the mosque and opened fire.
IS, which views some practices of the Sufi sect as heretical, had previously targeted the mystics by kidnapping one of their leaders and beheading him.
In one of their propaganda outlets, they had also vowed to fight the Sufis in Sinai, singling out the Jariri Sufi order associated with the mosque.
Sheikh Mohamed al-Jawish, deputy head of the Jariri order, said that less than a month ago jihadists visited Rawda mosque and spoke to the muezzin, Fethy Ismail, who issued the call to prayer five times a day.
"They entered the mosque. They were unknown" to the congregants, he told AFP.
He said they told the muezzin, who later died in the massacre: "Don't celebrate the Mawlid. Don't hold Sufi prayer circles."
Mawlids mark the Prophet Mohammed's birthday, and those of Muslim saints. IS follows the puritan Salafi theology and views the practice as an unlawful innovation in Islam.
Despite the warning, Jawish said no one expected IS would return and actually carry out a massacre which shocked even supporters of the jihadist group.
"No one expected this. They thought the issue ended with the warning not to hold the Sufi prayer circles," Jawish said in a phone interview.
IS has claimed attacks that have killed dozens of Sufis, most notably in Pakistan.
If the mosque was attacked because of its Sufi connections, the massacre would be in line with IS in Egypt increasingly focusing on civilian targets as it makes little headway in its Sinai insurgency.
IS has killed hundreds of policemen and soldiers in the Sinai, as well as civilians accused of working with the authorities, since the July 2013 ouster of Islamist president Mohamed Morsi.