Today is Gimmel Tammuz. This is the 13th anniversary of when the Lubavitcher Rebbe, Rabbi Menachem Mendel Schneerson of righteous memory passed away from creation.
(Source: http://www.chabad.org/generic.asp?aid=142232)
It is a popular observance among Chabad Chassidim to go to the Rebbe’s Ohel during Gimmel Tammuz. For more customs and observances, see here.
You can send a prayer request either by fax (718) 723-4444, visiting the Ohel if you are in the New York area, or filling in this form.
