The best sacrifices are the most expensive and the fattest

Abu al-Aswad al-Sulami narrates from his father, and he from his grandfather (may Allah be pleased with him), that he said: I was the seventh of seven people with the Messenger of Allah (peace and blessings be upon him) on a journey when Eid al-Adha came. The Messenger of Allah (peace and blessings be upon him) gave us an instruction, so each one of us collected one dirham, and we bought a sacrificial animal for seven dirhams. We said: O Messenger of Allah (peace and blessings be upon him)! We have bought it at a high price. He (peace and blessings be upon him) said: "Indeed, the best sacrificial animals are those that are the most valuable and the fattest." The narrator said: Then the Messenger of Allah (peace and blessings be upon him) gave us an instruction, so one man took hold of one leg, another of the other leg, a third of one foreleg, a fourth of the other foreleg, a fifth of one horn and a sixth of the other horn, while the seventh slaughtered it, and all of them together said the takbir over it.

Mu'awiyah bin Qurrah narrates from his father (may Allah be pleased with him) that a man said: O Messenger of Allah (peace and blessings be upon him)! When I am about to slaughter a goat, I feel pity for it. The Messenger of Allah (peace and blessings be upon him) said: "If you show mercy to it, Allah Almighty will show mercy to you."
This hadith has an authentic chain (sahih al-isnad), but the two Shaykhs (Bukhari and Muslim) did not record it.