1. Columbia University Rare Book & Manuscript Library, MS X893.19 K71 no. 22 DS ID: DS18730 Title: Letter and Hebrew text Author: Menahem Mendel Krengel Place: Ukraine Date: 186-
2. Columbia University Rare Book & Manuscript Library, MS X893.19 K71 no. 23 DS ID: DS18731 Title: Letter and Hebrew text Author: Yitzchak Elchanan Spektor Place: Ukraine Date: 186-