Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 203
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 203, with English translation by Maimonides (Rambam).
להקים המשא על הבהמה, שנאמר: "הקם תקים, עימו" (דברים כב,ד).
To [help a colleague] load a burden unto a beast, as [Deuteronomy 22:4] states: " You shall lift it up with him."