Mishnah Berurah — משנה ברורה

Onto another garment - But if he wants to [re]attach the corner [back] onto the garment that it tore from, even if it tore off completely and it's not attached even slightly, he does not need to untie the ציצית [first], and it [would] not [be] invalidated because of "Make it, and not from that which is [already] made" since it's original "making" on this garment was valid. And all this is as long as the garment did not become a 3 cornered garment when it tore (ie. when the corner tore off, it happened in such a way that the garment now has only 3 corners), as was seen above in se'if katan 6; and also specifically if the corner [that tore off] is at least 3 finger-widths by 3 finger-widths, as is seen nearby in se'if 4. All of this is according to the Shulchan Aruch and the Magen Avraham in se'if katan 3. But the Ta"z in se'if katan 3 rules that there is no difference if the attaching [of the detached corner] is to a different garment, or to this [garment that it tore from] itself; it's all under the same category of "Make it, and not from that which is [already] made", and one should be stringent [regarding this] and so did the Derech Hachaim rule.