12 Nissan 5707

Here is a letter from R' Shmuel Zalmanov to rabbonim on behalf of Vaad Shomrei Shabbos encouraging them to speak about shmiras shabbos in their shuls and to establish shiurim in hilchos shabbos.

11 Nissan 5721

Here is a letter from the Rebbe to R' Yaakov Nosson Rubin dated 11 Nissan 5721.

11 Nissan 5726

Here is a letter from the Rebbe to R' Moshe Yitzchok Hecht dated 11 Nissan 5726.