What is the source in the Talmud for what Lashon hara is? How do we know how to define it? How do we explain, what seemingly appears to be lashon hara between Tanaim and Amoraim. For example Shabbos 53a when Shmuel says of Rav “he doesn’t know anything about matters of Shabbos”
What is the halachic source in the Talmud that the tikkun for lashon hara is asking someone to forgive you? Wouldn’t telling someone you spoke lashon hara make it worse, and eventually lead to more lashon hara, possibly about others who also spoke lashon hara about this person..?
Are there no other sources other than the Chafets Haim who codify these halachot?
There are many passages in the Talmud and the Midrashic literature that include sharp expressions such as “it appears he has no brain in his skull” (Yevamos 9a; Menachos 80b) and similar quips.
This is not considered lashon hara, because the expressions were stated in the heat of a Talmudic debate, and not meant as offensive and derisory statements, but only as making the point forcefully.
The Chafetz Chaim addresses these questions in his Sefer (Be’er Mayim Chaim 8:23), and writes that the expressions are intended to reinforce the position and to ensure that others will not follow the wrong halachic position.
There are no other sefarim that really codify the laws of Lashon Hara, because before the Chafetz Chaim published his work the entire are was seen as being ethical (mussar) rather than halachic (the Rambam writes on Lashon Hara in his Laws of De’os). This does not make the area any lighter or more lenient, but the Chafetz Chaim transformed it in forming a legal code of law, which had not been done before.