Positive commandment · Mitzvat Aseh #242 of 613
To render judgment [in questions] regarding an unpaid watchman
לדון בדין שומר חינם
The verse · Shemot 22:6
כִּי־יִתֵּן אִישׁ אֶל־רֵעֵהוּ כֶּסֶף אוֹ־כֵלִים לִשְׁמֹר וְגֻנַּב מִבֵּית הָאִישׁ אִם־יִמָּצֵא הַגַּנָּב יְשַׁלֵּם שְׁנָיִם
“If a man shall deliver to his neighbour money or vessels to keep, and it be stolen out of the man’s house; if the thief be found, he shall pay double.”
The Rambam’s words
To render judgment [in questions] regarding an unpaid watchman, as [Exodus 22:6] states: "If a person will give a colleague money or utensils [to watch]...."
לדון בדין שומר חינם, שנאמר: "כי ייתן איש אל ריעהו כסף או כלים" (שמות כב,ו).
Why · Sefer HaChinuch #57
The commandment on the court to judge the case of an unpaid guardian
“The root is well-known.”
Who & when
“And [it] is practiced in every place and at all times.”
Where in the Mishneh Torah
Hilchot Borrowing and Deposit הלכות שאלה ופיקדון