It is permissible to have a Canaanite slave perform excruciating labor.Although this is the law, the attribute of piety and the way of wisdom is for a person to be merciful and to pursue justice, not to make his slaves carry a heavy yoke, nor cause them distress. He should allow them to partake of all the food and drink he serves. This was the practice of the Sages of the first generations who would give their slaves from every dish of which they themselves would partake. And they would provide food for their animals and slaves before partaking of their own meals. And so, it is written Psalms 123:2: "As the eyes of slaves to their master's hand, and like the eyes of a maid-servant to her mistress' hand, so are our eyes to God."
Similarly, we should not embarrass a slave by our deeds or with words, for the Torah prescribed that they perform service, not that they be humiliated. Nor should one shout or vent anger upon them extensively. Instead, one should speak to them gently, and listen to their claims. This is explicitly stated with regard to the positive paths of Job for which he was praised Job 31:13, 15: "Have I ever shunned justice for my slave and maid-servant when they quarreled with me.... Did not He who made me in the belly make him? Was it not the One who prepared us in the womb?"
Cruelty and arrogance are found only among idol-worshipping gentiles. By contrast, the descendants of Abraham our patriarch, i.e., the Jews whom the Holy One, blessed be He, granted the goodness of the Torah and commanded to observe righteous statutes and judgments, are merciful to all.
And similarly, with regard to the attributes of the Holy One, blessed be He, which He commanded us to emulate, it is written Psalms 145:9: "His mercies are upon all of His works." And whoever shows mercy to others will have mercy shown to him, as implied by Deuteronomy 13:18: "He will show you mercy, and be merciful upon you and multiply you."