Responsa על בבא בתרא 120:1

They responded: 'Such an argument need not enter here' (Bava Metzia 16a:18), since the Torah says "In order that you shall remember" (Numbers 15:40).³Therefore there is a positive commandment to perform an action of remembering, namely, to wear tzitzit. "Nonetheless, leave the Jews alone, it is better than they sin unintentionally than intentionally." (Bava Batra 60b:21)

Q. B's building was contiguous to A's property. The foundation of this building extended two hand-breadths beyond the wall itself. B wanted to build another wall in line with the edge of this foundation, the wall to extend two hand-breadths beyond the existing wall. A protested vigorously claiming that B's property ended at the edge of the wall of the building mentioned above, and that the foundation of such building extended two hand-breadths in his (A's) property.
A. Since B was in undisturbed possession of the width of the foundation, he was thus in possession of the disputed two hand-breadths of ground along the whole length of the property, and upwards reaching into the sky. Therefore, if B will take an oath to the effect that he did not remove his neighbor's landmark [when the foundation was built], the disputed two hand-breadths of ground will belong to him. Although according to Biblical law no oath is administered in disputes involving real property, such an oath is required by Rabbinic enactment.
SOURCES: Cr. 239; Am II, 184; Mord. B. B. 558; Agudah B. B. 109.