Reference for Bava Metzia 152:6
היה יפה ששה דינרים נותן להן סלע או יגמרו מלאכתן ויטלו שני סלעים ואם סלע נותן להם סלע
For it has been taught: If one hires labourers and they deceive the employer, or the employer deceives them, they have nothing but resentment against each other [but no legal redress]. Now, this holds good only if they have not gone [to the scene of their labour]; but if ass-drivers [are engaged to convey a load of grain from a certain place and] go [there] and find no grain, or labourers [hired to plough a field] go and find the field a swamp [unfit for ploughing], he must pay them in full; yet travelling with a load is not the same as travelling empty-handed, nor is working the same as sitting idle.<span class="x" onmousemove="('comment',' I.e., though the labourers can claim for the loss of the day's work, and the ass-drivers likewise, a man is always prepared to accept somewhat less than a full day's wages if he is permitted to be idle that day, and it is only to that lesser sum that they are entitled. ');"><sup>6</sup></span>