Three letters from Rabbi Chaim Yaakov Naftali Silberberg, 1900, 1908, 1910. Rabbi Chaim Naftali Silberger [1850-1930] was known as Rabbi Naftali Warsawer, he was a mo”tz in Warsaw for many years and was heavily involved in explaining and editing the works of Maharal Tzintz. He was very close to gedolei yisrael of all factions, and was a special friend of the Chofetz Chaim and the Imrei Emes of Ger. Refer to Otzar HaRabbanim 6416, 6528