I have seen that some sing Shoshanas Yaakov on Pesach to commemorate the death of Haman. Can someone please direct me to an authoritative source for this custom?
See references to it here: http://www.theyeshivaworld.com/coffeeroom/topic/how-do-you-commemorate-the-death-of-haman http://www.theyeshivaworld.com/coffeeroom/topic/when-did-haman-die