Halakhah к Берешит 37:2

And the descent of Israel into Egypt, too, stemmed initially from this [i.e., from lashon hara], viz. (Bereshith 37:2): "And Joseph brought evil report of them [the sons of Leah] to their father," whence it was decreed by Heaven, measure for measure, that he be sold into slavery, his having accused them of calling their brothers [from the maidservants] "slaves" (viz. Bereshith Rabbah 84:7 and Yerushalmi Peah 1:1). Though Joseph had a heter [halachic license] for bringing this "evil report," as the exegetes explain, it is to be noted that this heter did not avail him [and he was sold into slavery].