In Rav Albo's Sefer HaIkkarim-Maamar 4.30.10 we read:
"The second opinion is that though the perfectly righteous get material reward in this world, yet since their number is small, and the great majority of righteous men do not get corporeal reward in this world, there should be in the next world corporeal as well as spiritual reward. This comes, they say, after the resurrection when the soul and the body will exist in conjunction, but without food and drink, as Moses lived forty days and forty nights with body and soul without eating and drinking. This is what, according to them, the Rabbis call the world to come, when they say concerning the righteous that they are prepared for the life of the world to come. They believe at the same time that the human soul does not die when the body dies, but that there is a stage of existence called Gan Eden (Paradise) where, immediately after death, the souls of the righteous are kept until they rise in resurrection and obtain the life in the world to come after the resurrection. This is what the Rabbis mean when they relate concerning Rabban Simon ben Gamaliel that he said to Rabbi Ishmael, who was weeping when he was condemned to die: Master, why weepest thou? In a brief moment thou wilt be placed in Gan Eden in the community of the righteous. We are also told that Rabbah bar Rab Huna said concerning Rabbah bar Shela, who died a short time before him: He preceded me in Gan Eden by a brief hour. This is the opinion of Nahmanides, of R. Meir Halevi, and a number of modern writers who follow them, may they all be blessed".
Do you know what sources Rav Albo draws from for the two aforementioned episodes of Rabban Simon ben Gamaliel and Rabbi Ishmael on the one hand, and Rabbah bar Rab Huna and Rabbah bar Shela on the other?