Is it permissible to combine the sacrifice of a vow (Nathr) and the sacrifice of an Eid (Uḍḥiyah) in a single animal?

Fulfilling a vow is obligatory. The Udhiyah (sacrifice) is a confirmed Sunnah according to the majority of scholars. One animal is not sufficient for both; rather, two animals must be slaughtered, one for each, separately.