Midrash for Shabbat 24:1
מִי שֶׁהֶחְשִׁיךְ בַּדֶּרֶךְ, נוֹתֵן כִּיסוֹ לְנָכְרִי, וְאִם אֵין עִמּוֹ נָכְרִי, מְנִיחוֹ עַל הַחֲמוֹר. הִגִּיעַ לֶחָצֵר הַחִיצוֹנָה, נוֹטֵל אֶת הַכֵּלִים הַנִּטָּלִין בְּשַׁבָּת, וְשֶׁאֵינָן נִטָּלִין בְּשַׁבָּת, מַתִּיר אֶת הַחֲבָלִים, וְהַשַּׂקִּין נוֹפְלִין מֵאֲלֵיהֶם:
If it were getting dark for one on the road (on Sabbath eve), he gives his purse to a gentile [while it is still day. And even though he becomes the Jew's messenger to carry his purse on Shabbath, it is axiomatic with the rabbis that a man will not contain himself when his money is at stake, and if this (the above) were not permitted, he would come to carry it four cubits in the public domain.] And if there is no gentile with him, he places it on an ass. [But if there is a gentile with him, he gives it to the gentile. Why so? For one is commanded vis-à-vis the resting of an ass, but not vis-à-vis the resting of a gentile. And when he places his purse on the ass when it gets dark, he does so while it is walking; that is, after it lifted its legs to walk, so that it does not perform akirah. And when the animal is going to stop, he removes it from her. And when she again lifts her legs to walk, he again places it upon her — this, so that the animal not perform akirah and hanachah. For if he is allowed to perform akirah and hanachah with him driving and leading it, he is "mechamer" (driving a laden beast) on Shabbath, which is forbidden whatever the beast is carrying, viz. (Exodus 20:10): "You shall not perform any labor, you … and your beast." Which labor is it that is performed jointly between a man and his beast? Mechamer.] When he reaches the outer courtyard [of the city, the first guarded place — When he comes to unload the ass] he takes [from it with his hand] vessels which may be moved on Shabbath. And (to release) those which may not be moved on Shabbath, he frees the [saddle] ropes, and the sacks fall of themselves.