When Rabbi Dov Baer of Lubavitch (1773-1827)  was a young father, he and his wife and children lived in the same house as his father, Rabbi Schneur Zalman (1745-1813). Rabbi Dov Baer and his family lived on the ground floor of the house and Rabbi Schneur Zalman lived above them on the second floor. Legend has it that one night, while Dov Baer was immersed in Torah study, his youngest child fell out of his cradle and began crying. Dov Baer heard nothing. But his father, Schneur Zalman, who was upstairs, also immersed in Torah study, heard his grandchild crying.  Without hesitation, Schneur Zalman stopped studying, came downstairs, lifted the infant from the floor and comforted him. Within no time, the baby was sleeping soundly. Schneur Zalman placed him in the cradle.  After a few minutes he left the nursery and went to speak to his son, Dov Baer, who remained immersed in his…