Source of Requirement
1. There is a positive Torah commandment to place Tzitzit strands on a four cornered garment that one wears.  2. There is, however, no obligation to wear such a garment in the first place. Nevertheless, our Rabbis have strongly promoted the observance of this relatively simple Mitzvah since it comes with great reward.
- Bamidbar 15:38; Devarim 22:12
- Rambam Hilchot Tzizit 3:11; Tur 24:1; Shulchan Aruch 24:1