Reference for Bava Metzia 63:11
דאי סלקא דעתך משמרת השתא משכח לה אבראי מעייל לה לגואי משכח לה מגואי מבעיא אלא שמע מינה אינה משמרת שמע מינה:
IF HE [THE OWNER OF THE ANIMAL] WENT, SAT DOWN AND SAID [TO THE PASSER-BY], 'SINCE THE OBLIGATION RESTS UPON YOU, IF YOU DESIRE TO UNLOAD, UNLOAD:' HE [THE PASSER-BY] IS EXEMPT, BECAUSE IT IS SAID, 'WITH HIM'; YET IF HE [THE OWNER] WAS OLD OR INFIRM HE IS BOUND [TO DO IT HIMSELF]. THERE IS A BIBLICAL PRECEPT TO UNLOAD, BUT NOT TO LOAD. R. SIMEON SAID: TO LOAD UP TOO. R. JOSE THE GALILEAN SAID: IF IT [THE ANIMAL] BORE MORE THAN HIS PROPER BURDEN, HE [THE PASSER-BY] HAS NO OBLIGATION TOWARDS HIM [ITS OWNER], BECAUSE IT IS WRITTEN, [IF THOU SEE THE ASS OF HIM THAT HATETH THEE LYING] UNDER ITS BURDEN, WHICH MEANS, A BURDEN UNDER WHICH IT CAN STAND.