1. Imam Baqir (as) says :
"The Sheikhayn (Abu Bakr and Umar) left the world and never repented and never felt shame face for what they did with Ameer ul Momineen (as) so Allah and his angels curse both of them"
Al Kafi, v 8, pg 246
Allamah Majlisi termed this hadith to be AUTHENTIC
Mirat ul Uqool, V 26 Pg 215
2. Imam Baqir (as) :
"Behind this sun there is forty suns between each sun is a time of forty years (distance). Over there is many people who dont know whether Allah created Adam or not. And behind this moon of your there is forty moons between each moon is the time of fourty years (Distance) and over there is many people who don't know whether Allah created Adam or no. They have been inspired just like how the bees have been inspired to curse the first (Abu Bakr) and second (Umar) continually all the time. And Allah has supervised angles for them that when whenever they don't curse them (Umar and Abu Bakr) they will be punished"
Basair al Darajaat Vol 2 pg 434
3. Muhaqqiq Al Bahraini writes in regards to one of our eminent Ulema of the past, Muhaqiq al-Karaki :
"And he [Al Karaki] didnt ride and he didnt do anything [except that] with his voice he cursed the Shaykhain [Abu Bakr and Omar] and those who follow their steps (ie. Ahle Tasannun)"
al-Muhaqiq al-Bahrani in his work Luluat al-Bahrain, pg 148