R. Abbahu said that R. Eleazar said: The fire of Gehinnom has no power over the Scholars. It is an ad majus conclusion [to be drawn] from the salamander.*
If now [in the case of] the salamander, which is [only] an offspring of fire, he who anoints himself with its blood is not affected by fire, how much more so the Scholars, whose whole body is fire, for it is written [Jer. 23, 29]: "Is not My word like as fire? saith the Lord".
Resh Lakish said. The fire of Gehinnom has no power over the transgressors of Israel.
Tractate Chagigah 27A.
A fabulous animal generated in fire which, according to the Midrash, must burn incessantly for seven days and nights; but Rashi here postulates seven years, and the Aruch (s.v.) seventy years. For a fun account of the legend, v. J. E. vol. X, pp. 646-7