שלום וברכה!
[כ"א שבט תשכ"א]
... לשאלתו בשם מר... אודות קניית שערס, לכל הראש יש לברר האם אין בזה איסור ריבית, כיון שכנראה מכתבו, החברה היא אך ורק של בני ישראל, ובפרט ע"פ דברי רז"ל שריבית מושכת אחרי' גם הקרן וכו'...
נדפסה בלקו"ש חכ"ד ע' 455.
Shalom u'Vrachah!
In response to your question on behalf of Mr. ... regarding buying shares, first and foremost it is necessary to clarify whether there is any prohibition of ribis (interest), since, as it appears from your letter, the company is comprised solely of Jews. Especially in light of our Sages' words that ribis draws after it even the principal, etc.
Summary
The Rebbe teaches that when investing in Jewish-owned companies, one must carefully investigate potential issues of ribis (interest), as such concerns can impact both profit and principal. Halachic guidance is essential for proper financial conduct.