"...Another thing: "A kindly man benefits himself", this refers to Hillel the Elder, that when he departed from his students, he would walk and they would walk with him. His students said to him: "Rabbi, where are you going to?" He said to them: "To do a kindness with a guest in my house." They said to him: "Every day you have guests?" He said to them: "After all, is not this poor soul a guest in the body? One day she's here, the next she's there [i.e., not in the body]." (Vayikra Rabbah 34:3)
Rabbi Eliezer was a student of Rabban Yochanan ben Zakkai (see here, for example), who was a student of Hillel the Elder himself (see here, for example) and also received some teachings from Shammai (see here). Interestingly, Rabbi Eliezer himself was considered a member of Beit Shammai1. In the Talmud, Tractate Shabbat 152b, it says:
"It was taught in a baraita that Rabbi Eliezer says: The souls of the righteous are stored beneath the Throne of Glory, as it is stated: “And the soul of my lord shall be bound in the bundle of life” (I Samuel 25:29). And the souls of the wicked are continuously tied up, and one angel stands at one end of the world and another angel stands at the other end of the world and they sling the souls of the wicked back and forth to one another, as it is stated: “And the souls of your enemies He shall sling out in the hollow of a sling” (I Samuel 25:29)."
and it is known that Rabbi Eliezer never taught anything that he hadn't heard from his own teacher, so he must have heard this idea from Rabban Yochanan, and the same thing is said about him, so that means that this idea came from Hillel (or maybe Shammai, or both).
This one may be a stretch, but Aquilas the Convert was a student of Rabbi Yehoshua and Rabbi Eliezer and was commissioned by them to produce a Greek Targum to the Bible, which received much praise from them2. Rabbi Yehoshua was a student of Beit Hillel3 and Rabbi Eliezer of Beit Shammai. Only fragments of Aquilas's commentary remain. One of the fragments, preserved in Shir Ha'Shirim Rabbah 1:3 and Kohelet Rabbah 1:11, reads:
"Another thing, "evermore" - Aquilas translated "athanasia", a world without death, and they would signal to one another with their fingers and say: ""For God—He is our God forever; He will lead us evermore", in two worlds He will lead us, in this world and in the next world. In this world, as it says: "For the LORD your God will bless you" and in the next world, as it says: "The LORD will guide you always"."
Yonatan ben Uziel was considered Hillel's top student. According to tradition, he authored the Aramaic Targum on the Prophets (hence it is called Targum Jonathan/Yonatan). On the verse brought by Rabbi Eliezer in the second source, Samuel 1:25:29, "And if anyone sets out to pursue you and seek your life, the life of my lord will be bound up in the bundle of life in the care of the LORD...", he translates it:
"And if anyone sets out to pursue you and seek your life, the soul of my lord will be stored in the next world before the LORD your G-d; but He will fling away the lives of your enemies as from the hollow of a sling."
1 The term used to relate Rabbi Eliezer to Beit Shammai is "Shammuti", which is clarified in the Jerusalem Talmud as referring to students of Beit Shammai (though ultimately, in both Talmuds, the only one referred to as such was Rabbi Eliezer). For example, it says in Tractate Terumot of the Jerusalem Talmud, 28a:
"...and if you shall say, Beit Hillel will admit and agree with Beit Shammai...Rabbi Eliezer says: "It should be raised and burned." - but isn't Rabbi Eliezer a Shammuti?!"
In context, the question of the Talmud on Rabbi Eliezer's view can only be understood if the term "Shammuti" means that he's of Beit Shammai, and seemingly he's disputing their view.
2 As it says in the Jerusalem Talmud, Tractate Megillah 10b:
"Aquilas the Convert translated the Torah before Rabbi Eliezer and before Rabbi Yehoshua and they lauded him and said: "You are fairer than all men"."
3 This is based on a mishna in Tractate Eduyot 1:14 which brings a dispute between Beit Hillel and Beit Shammai. This same dispute is brought in the Tosefta, Tractate Ohalot 5:10, in the name of Rabbi Yehoshua and Beit Shammai (including one particular anonymous student of Beit Shammai), thus we know that Rabbi Yehoshua was part of Beit Hillel.