What is the ruling of the Shari'ah regarding the ill-treatment of domestic workers?

Servants must be treated with gentleness and kindness, and harming them through word or deed must be avoided, for they are human beings with feelings and emotions. A Muslim should be good to them in their food and clothing, and he will be held accountable for them on the Day of Resurrection. It is narrated in Musnad Ahmad, on the authority of Umar ibn al-Khattab, that a man asked the Messenger of Allah, peace and blessings be upon him, about striking his misbehaving servant, and he replied: "Forgive him seventy times every day."