As quoted from:
Shulchan HaMelech, a Kitzur Shulchan Aruch in 3 volumes as compiled by Maharan HaRav Shmuel Laniado z'al, 1923 with the supplement "Al HaShulchan" containing various opinions compiled by Ezra Basri, Chief Justice of the District Court, Jerusalem in 1992.
We would also like to dedicate this learning for the speedy and complete recovery of our friends' 5-year-old son, Joseph Benjamin, son of Ireneusz Khrystof, diagnosed in April with ALL leukemia. Please have him in mind when studying.
p. 28 Chapter Nine
7. b. One should wear the tallit kattan over the undershirt and sleep in it, only removing it in the bathhouse (Bet Simcha p. 79)
Note from us: Please consult your own rabbi to find out what to do - these are for learning purposes only.