Saeed, mastermind of the 2008 assault on Mumbai, offered 'ghayabana namaz-e-janaza' (funeral prayers in absentia) for Kasab at the conclusion of a two-day training session of the Jamaat-ud-Dawah at its headquarters at Muridke near Lahore.
The event was attended by thousands of people, the Urdu newspaper Daily Express reported.
It did not say when the event was held.
25-year-old Kasab, who was part of a team of 10 Lashkar-e-Taiba terrorists who killed 166 people during three days of carnage in Mumbai four years ago, was hanged in a Pune jail on Wednesday.
The Pakistani Taliban have threatened to target Indians to avenge Kasab's execution.
The LeT has described Kasab as a "hero" who will inspire more terror attacks.
Shortly after Kasab's hanging, the JuD refused to comment on the issue.
"We have decided not to issue any statement on the hanging of Kasab as we think it is not appropriate," Habibullah Salfi, a member of the JuD's media arm, told PTI.
The JuD claims it has no links with LeT.
Following the Mumbai attacks, the UN Security Council had declared the JuD a front for the banned LeT.
Earlier this year, the US offered a 10-million-dollar bounty for Saeed.
