Ibn Abbas narrated
"A man had laid down his sheep (in preparation to slaughter it) and then he went about sharpening his knife. Upon seeing this, the Messenger of Allah rebuked him saying: 'Do you want to kill it twice? Wouldn't it have been better for you to sharpen your knife before laying it down (so as not to terrorize it)?' " (Narrated by Al-Tabarani and Al-Hakim)
Shaddad ibn Aws said
"Two are the things which I remember Allah's Messenger (pbuh) having said: 'Verily Allah has enjoined goodness to everything; so when you kill, kill in a good way and when you slaughter, slaughter in a good way. Every one of you should sharpen his knife, and let the slaughtered animal die comfortably.' " (Narrated by Muslim)
Muhammad (pbuh) also used to command mercy for all animals such that they are fed well, watered well, not forced to carry too heavy a burden, and not tortured or maimed for one's enjoyment.
"The Messenger of Allah, may Allah bless him and grant him peace, said, 'While a man was walking on a road he became very thirsty. He found a well, went into it, drank, and came out. [Upon exiting he met] a dog panting and eating the dirt out of thirst. The man said: 'This dog has become stricken with the same degree of thirst which had stricken me.' He went down into the well and filled his shoe and then held it in his mouth until he climbed out and gave the dog water to drink. Allah thanked him (for his good deed) and forgave him.' They said, 'O Messenger of Allah, are we rewarded for taking care of beasts?' He said, 'There is a reward [for you] in every creature with a moist liver.'"(Narrated by Al-Bukhari, Muslim, and Malik)
"Allah's Messenger (pbuh) said: 'A woman was punished because of a cat. She neither provided it with food nor drink, nor set it free so that it might eat the insects of the earth.' " (Narrated by Muslim and Al-Bukhari).
Sahl ibn Amr said
"The Messenger of Allah passed by a camel who's stomach quite touched it's back (from lack of food). Upon seeing this he said: 'Fear God in these unspeaking animals! Ride them [while they are] in good health, and eat them [while they are] in good health' " (Narrated by Abu-Dawood)
Regarding slaves, when Muhammad (pbuh) became the messenger of Allah the people of his land had become accustomed to having countless slaves and usually treated them quite harshly. During the period of his prophethood he worked diligently to do what he could to cut down on their numbers. Islam closed most of the doors leading to slavery and encourages the freeing of slaves in many ways. For those people who continued to posses slaves they were encouraged to treat them fairly and with mercy.
"The Prophet (pbuh) said: 'Feed those of your slaves who please you from what you yourselves eat and clothe them with what you clothe yourselves, but sell those who do not please you and do not punish Allah's creatures.' " (Narrated by Abu-Dawood)
Ma'rur narrated that
"I saw AbuDharr wearing a Burd (garment) and his slave too was wearing a Burd, so I said (to AbuDharr), 'If you take this (Burd of your slave) and wear it (along with yours), you will have a nice suit and you may give him another garment.' AbuDharr said, "There [once] was a quarrel between me and another man whose mother was a non-Arab and I called her bad names. The man complained about me to the Prophet (pbuh). The Prophet (pbuh) said, 'Did you abuse so-and-so?' I said, 'Yes.' He said, 'Did you call his mother bad names?' I said, 'Yes.' He said, 'You still have the traits of (the pre-Islamic period of) ignorance.' I said, '(Do I still have ignorance) even now in my old age?' He said, 'Yes, they (slaves or servants) are your brothers and Allah has put them under your command. So the one under whose hand Allah has put his brother, should feed him from what he eats, and clothe him in what he wears, and should not ask him to do anything beyond his capacity. And if ever he asks him to do a hard task, he should help him with it.'" (Narrated by Al-Bukhari)
Abdullah ibn Umar said
"An A'arabi (desert Arab) came to the Prophet of Allah (pbuh) and said: 'O Messenger of Allah, how many times should I forgive my slave every day?' The Prophet (pbuh) replied: 'Seventy times.' " (Narrated by Al-Tirmathi and Abu-Dawood)
Abdullah ibn Umar also narrated
"The Messenger of Allah (pbuh) said: 'Pay the worker his [due] wages before his sweat dries' " (Narrated by ibn Majah)