halacha - Where in halachah does it say that one is forbidden to go onto the Har HaBayis?

1) Rav Elyashiv zt”l stated in 2009, “Halacha forbids going onto Har HaBayis but today, it is more than this, it is an act that may lead to a religious war and bloodshed."

Where in halacha does it say that going onto the Har HaBayis is forbidden?

2) Rav Kanievsky wrote that, “Entrance to the Temple Mount and the defilement of the Holy of Holies, is more severe than any of the violations in the Torah.”

Is there any halachic source for this?

3) Rav Dovid Yosef says, “… One who davens there his tefilos are to’eva (an abomination) to Hashem are not welcomed but blasphemous and one who is guilty of this commits a major avreira.”

Is there any halachic source for this?

Answer

The Rambam in Sefer haMitzvos says in מצוה עח:

שהזהיר לכל טמא להכנס תוך מחנה לוייה שכמוהו לדורות הר הבית

That the Torah commands us not to go into the Levite camp if one is impure, which corresponds to Har Habayit in our times.

So here we seem to have a source.

The Rambam refers to the Mishna in כלים Mishna 1:8 as his source. There it says:

הַר הַבַּיִת מְקֻדָּשׁ מִמֶּנּוּ, שֶׁאֵין זָבִים וְזָבוֹת נִדּוֹת וְיוֹלְדוֹת נִכְנָסִים לְשָׁם. הַחֵיל מְקֻדָּשׁ מִמֶּנּוּ, שֶׁאֵין גּוֹיִם וּטְמֵא מֵת נִכְנָסִים לְשָׁם.‏

Har HaBayit is holier [than the city of Jerusalem] in that Zavim, Zavot, Nidot and Yoldot [who'se impurity is stricter than that of a Tamei Mes שטומאתן חמורה מטומאת מת, שעושות משכב ומושב ומטמאות באבן מסמא מה שאין כן בטומאת מת] are not allowed in.

The Cheil is holier than Har haBayit in that non-Jews and those impure because they came into contact with a dead body are not allowed in. (The Cheil was a low wall that surrounded that Temple, inside the Har HaBayit.)

This does not seem to match what the Rambam says.

The Rambam also Paskens in הלכות ביאת המקדש - פרק שלישי the same, way - and summarises in his introduction:

ז) שֶׁלֹּא יִכָּנֵס טָמֵא לַמִּקְדָּשׁ. ח) שֶׁלֹּא יִכָּנֵס טָמֵא לְהַר הַבַּיִת.

ג: וּמְשַׁלְּחִין זָבִין וְזָבוֹת נִדּוֹת וְיוֹלְדוֹת חוּץ לִשְׁתֵּי מַחֲנוֹת שֶׁהוּא חוּץ לְהַר הַבַּיִת. מִפְּנֵי שֶׁהֵן מְטַמְּאִין הַמִּשְׁכָּב וְהַמּוֹשָׁב אֲפִלּוּ מִתַּחַת הָאֶבֶן מַה שֶּׁאֵין הַמֵּת מְטַמֵּא: ‏

ד: טְמֵא מֵת אֲפִלּוּ הַמֵּת עַצְמוֹ מֻתָּר לְהִכָּנֵס לְהַר הַבַּיִת שֶׁנֶּאֱמַר (שמות יג-יט) 'וַיִּקַּח משֶׁה אֶת עַצְמוֹת יוֹסֵף עִמּוֹ' עִמּוֹ בְּמַחֲנֵה הַלְּוִיָּה:‏

So we need to assume that R' Elyashiv זצ"ל considered us all possible Zavim/Zavot (who cannot enter the Har HaBayit until they bring a Korban). Otherwise we'd have the ridiculous assumption that his source is some summaries but not the details of the Rambam.