As I Heard Them, Vol. 1, p. 301, no. 33
Another account my zeide heard from the Tzemach Tzedek’s children:
“Late into the night,” their father told them, “I discussed with Reb Aizel subjects which stand at the loftiest heights. Afterwards I went to rest — but then resolved to take a look at ‘the zeide’s [the Alter Rebbe’s] soldier.’ He was standing, studying Gemara like a diligent young scholar who hadn’t learned for a long time.”