Mishneh Torah (Rambam) משנה תורה

A garment to which the Torah obligates a person to attach tzitzit [must meet the following requirements]: a) it must have four - or more than four - corners; b) it must be large enough to cover both the head and the majority of the body of a child who is able to walk on his own in the marketplace without having someone else accompany him and watch him; c) it must be made of either wool or linen alone.

In contrast, a garment made of other fabrics - for example, clothes of silk, cotton, camels' wool, hares' wool, goats' wool, and the like - are required to have tzitzit only because of Rabbinic decree, in order to show regard for the mitzvah of tzitzit. [These garments require tzitzit only] when they are four-cornered - or have more than four corners - and are of the measure mentioned above. [The motivating principle for this law] is that all the garments mentioned in the Torah without any further explanation refer to those made of either wool or linen alone.

On the four corners of your garments (Deuteronomy 22:12 : This applies to a garment which possesses four corners, but not to one which possesses only three. Perhaps, [it comes to include] a four-cornered garment and [to exclude] a five-cornered garment? The Torah continues: "with which you cover yourself." This includes even a five- (or more) cornered garment. Why do I obligate a garment of five corners and exempt a garment of three corners? Neither has four corners [as required by the above verse]. Because a five-cornered garment has four corners. Accordingly, when one attaches tzitzit to a garment with five or six corners, one should attach the tzitzit only to the four corners which are farthest apart from each other from among these five or six corners, as [implied by the phrase,] "On the four corners of your garments."

If a garment is made of cloth and its corners of leather, it requires tzitzit. If the garment is of leather and its corners are of cloth, it does not require tzitzit. The determining factor is the makeup of the garment itself. A garment belonging to two partners requires [tzitzit], as [implied by Numbers 15:38]: "On the corners of their garments." The term "your garments" [(Deuteronomy 22:12 , which is interpreted as an exclusion,] excludes only a borrowed garment, since a borrowed garment does not require tzitzit for thirty days. Afterwards, it does require them.

For a garment of wool, the white strands should be made of wool. For a garment of linen, the white strands should be made of linen. For garments of other [fabrics], the white strands should be made from the same fabric as the garment itself. For example, silk strands should be used for a silk garment, strands of goats' wool should be used for garments of goats' wool. If one desired to make white strands of wool or linen for [garments of] any type [of fabric], one may, because [strands of] wool and linen can fulfill the obligation [of tzitzit] for garments made of their own fabric or for garments made of other fabrics. In contrast, [strands made] from other fabrics can fulfill the obligation [of tzitzit] only for garments made of their own fabric.

What is the ruling regarding making woolen strands for a garment of linen or linen strands for a garment of wool - even though we are speaking only of the white strands without techelet? One might think that it should be permitted, because sha'atnez is permitted to be used for tzitzit, as evident from the fact that techelet is made using woolen strands, and yet it should be placed on a linen garment. Nevertheless, this is not done. Why? Because it is possible to make the white strands from the same fabric as [the garment]. Whenever [a conflict exists] between the observance of a positive commandment and the adherence to a negative commandment, [the following rules apply]: If it is possible to observe both of them, one should. If not, the observance of the positive commandment supersedes the negative commandment. In the present instance, however, it is possible to observe both of them.

Techelet should not be attached to a linen garment. Rather, one should [make the tzitzit] from white threads of linen alone. This is not because [the prohibition against] sha'atnez supersedes [the mitzvah of] tzitzit, but rather it is a Rabbinical decree [imposed] lest one wear the garment at night, when one is not required to wear tzitzit, and thus violate a negative commandment when the performance of a positive commandment is not involved. [This is because] the obligation to wear tzitzit applies during the day, but not at night [as can be inferred from Numbers 15:39]: "And you shall see them." [The mitzvah applies only] during a time when one can see. [Nevertheless,] a blind man is obligated to wear tzitzit. Even though he does not see them, others see him [wearing them].

A person is permitted to wear tzitzit at night, both during the weekdays and on the Sabbath, even though this is not the time when the mitzvah should be fulfilled, provided he does not recite a blessing. When should the blessing over tzitzit be recited in the morning? When [the sun has risen so] that one can differentiate between the strands of techelet and those which are white. Which blessing should be recited upon it? "Blessed are you, God, our Lord, King of the universe, who has sanctified us with His commandments and commanded us to wrap ourselves with tzitzit." Whenever a person wraps himself in tzitzit during the day, he should recite the blessing before doing so. No blessing should be recited on the tzitzit when making them, because the ultimate purpose of the mitzvah is that one should wrap oneself in [a tallit].

It is permissible to enter a lavatory or a bathhouse [wearing] tzitzit. If one of the strands of white or techelet becomes torn, it may be discarded in a garbage dump, because tzitzit is a mitzvah which does not confer sanctity on the article itself. It is forbidden to sell a garment with tzitzit to a gentile until he removes the tzitzit, not because the garment possesses a measure of holiness, but because we are concerned that he will dress in it, and [unknowingly,] a Jew will accompany him, thinking that he is a fellow Jew, and the gentile may kill him. Women, servants, and minors are not required by the Torah to wear tzitzit. It is, however, a Rabbinical obligation for every child who knows how to dress himself to wear tzitzit in order to educate him to fulfill mitzvot. Women and servants who wish to wrap themselves in tzitzit may do so without reciting a blessing. Similarly, regarding the other positive commandments which women are not required to fulfill, if they desire to fulfill them without reciting a blessing, they should not be prevented from doing so. A tumtum and an androgynous are obligated in all positive commandments because of the doubt [about their status]. Therefore, they fulfill [all these positive commandments] without reciting a blessing.

What is the nature of the obligation of the commandment of tzitzit? Every person who is obligated to fulfill this mitzvah, if he wears a garment requiring tzitzit, should attach tzitzit to it and then wear it. If he wears it without attaching tzitzit to it, he has negated [this] positive commandment. There is, however, no obligation to attach tzitzit to a garment which requires tzitzit, as long as it remains folded in its place, without a person wearing it. It is not that a garment requires [tzitzit]. Rather, the requirement is incumbent on the person [wearing] the garment.

Even though a person is not obligated to purchase a tallit and wrap himself in it so that he must attach tzitzit to it, it is not proper for a person to release himself from this commandment. Instead, he should always try to be wrapped in a garment which requires tzitzit so that he will fulfill this mitzvah. In particular, care should be taken regarding this matter during prayer. It is very shameful for a Torah scholar to pray without being wrapped [in a tallit].

A person should always be careful regarding the mitzvah of tzitzit, because the Torah considered it equal to all the mitzvot and considered them all as dependent on it, as [implied by Numbers 15:39]: "And you shall see them and remember all the mitzvot of God."