The sacrifice (udhiyah) is the sunnah of Prophets Ibrahim, Isma`il, and Muhammad (peace and blessings be upon them all). It reminds us of the great act of sacrifice that Prophets Ibrahim and Isma`il were willing to do for the sake of Almighty Allah. Allah spared the life of Prophet Isma`il, and He tells us that (We ransomed him with a momentous sacrifice.) (As-Saffat 37:107)
It is not recommended to sell furniture to buy the sacrificial animal. There is nothing wrong in borrowing money to buy it as long as one is able to repay that money.
To explain the ruling of this in more details, below is what Sheikh `Abdul-Bari Az-Zamzami said:
Offering udhiyah (sacrifice) during `Eid Al-Adha is sunnah and not obligatory. Abu Bakr and `Umar did not offer sacrifice during their caliphate to show the people that it is not obligatory. Therefore, a Muslim should not burden himself with what he cannot bear in order to get the money for the sacrifice. The Qur’an says: (Allah does not charge a soul except (with than within) its capacity) (Al-Baqarah 2:286) The Prophet (peace and blessings be upon him) said: “Of what I asked you to do, do it as much as you can.” (Muslim)
Therefore, selling house furniture to buy the sacrifice is not recommended because the furniture is an essential thing in the house and no one can do without it. As for borrowing money to buy the sacrifice, if the one who is going to get that money from others is sure that he will be able to pay it back when it is due, then there is nothing wrong in borrowing this money.