sources mekorot - The Medrash and Gemara about Hoshana Rabbah

I read on shirat devorah the following:

1) The Midrash tells us that G‑d told Abraham: “If atonement is not granted to your children on Rosh Hashanah, I will grant it on Yom Kippur; if they do not attain atonement on Yom Kippur, it will be given on Hoshana Rabbah.”

Where does the Midrash say this?

2) Isaiah says, “They seek Me day [after] day.”

Where does Isaiah say this?

The Talmud explains that these two “days” refer to the day when the shofar is sounded [Rosh Hashanah] and the day when we take the willow [Hoshana Rabbah]—the day when the heavenly judgment begins, and the day when it concludes.

Where does the Gemara say this?

Answer

Isaiah (58:2):

וְאוֹתִי, יוֹם יוֹם יִדְרֹשׁוּן, וְדַעַת דְּרָכַי, יֶחְפָּצוּן; כְּגוֹי אֲשֶׁר-צְדָקָה עָשָׂה, וּמִשְׁפַּט אֱלֹהָיו לֹא עָזָב, יִשְׁאָלוּנִי מִשְׁפְּטֵי-צֶדֶק, קִרְבַת אֱלֹהִים יֶחְפָּצוּן

The Yerushalmi Rosh Hashana (4:8) says:

ואותי יום יום ידרושון זו תקיעה וערבה

The reference is to the Aravah ceremony which was performed on the day known as Hoshana Rabba. I see no reference in the Yerushalmi to Hoshana Rabba as a day of judgement.

The Paneach Razza makes a brief reference to the Midrash about Avraham and Hoshana Rabba in Parshas Emor:

הושענה רבה וכמאמרם במדרש שאמר הקב"ה לאברהם אבינו וכו'