Abu Hurairah (radi'Allahu anhu) reported that Messenger of Allah (sall'Allahu alaihi wasallam) has said: "Whoever performs Hajj for the sake of pleasing Allah (Jalla Jalalahu) and therein utters no word of evil, nor commits any evil deed, then he returns from Hajj as pure and free from sins as on the day on which his mother gave birth to him." [Al-Bukhari and Muslim]
"At the time of the Messenger of Allaah (peace and blessings of Allaah be upon him), a man would sacrifice a sheep on behalf of himself and the members of his household, and they would eat from it and give some to others."
(Reported by Ibn Maajah and al-Tirmidhi, who classed it as saheeh)
The Prophet (peace and blessings of Allaah be upon him) said: "There are four that will not do for sacrifice: a one-eyed animal whose defect is obvious, a sick animal whose sickness is obvious, a lame animal whose limp is obvious and an emaciated animal that has no marrow in its bones ." (Saheeh, Saheeh al-Jaami', no. 886).