Muhammed bin Abi Haatim (rahimahullah) narrates the following:
When I would accompany Imaam Bukhaari (rahimahullah) on a journey, then we would stay in the same room, unless it was the summer season (when the heat would be intense).
During the night, I would notice that Imaam Bukhaari (rahimahullah) would get up approximately fifteen to twenty times. On getting up, Imaam Bukhaari (rahimahullah) would take the flint (a stone used for lighting fire) and use it to light the lamp. Thereafter, he would look at certain Ahaadith and make notes. After some time, he would place his head down and go back to sleep.
Noticing this, I said to him, “Why are you taking the trouble of waking up to do whatever work you wish? Why do you not wake me up so that I can serve you and assist you?” Imaam Bukhaari (rahimahullah) replied, “You are still young, so I do not wish to disturb your sleep.”
Muhammed bin Abi Haatim (rahimahullah) further mentioned that at the time of sehri, Imaam Bukhaari (rahimahullah) would perform tahajjud salaah followed by his witr salaah.
He also mentioned that Imaam Bukhaari (rahimahullah) possessed some of the blessed hair of Rasulullah (sallallahu ‘alaihi wasallam) which he would keep with him in his clothing (so that he could derive blessings and barakah from it).
(Hadyus Saari pg. 481)