19 Cheshvan 5781 AM
This month, 3695 years ago, in the year 2086 AM, Sarah Imeinu passed away.
The Midrash says Haman tried to figure out which month is the luckiest month, in order for him to succeed with his evil plan. Cheshvan he considered an unlucky month since in the month of Cheshvan Sarah Imeinu passed away.
It is interesting, the way the Midrash sees this – that the death of Sarah Imeinu, is a Z’chus for Klal Yisrael, unlike the month Adar. We know that Adar was chosen since this is the month when Moshe Rabeinu passed away, hence unlucky.
Source: Esther Rabba, 7:11