Sunan Ibn Majah
3463
Sahih+3

Anas bin Malik said:“I heard the Messenger of Allah (ﷺ) saying: ‘The cure for sciatica is the fat from the tail of a Bedouin sheep (or wild sheep), which should be melted and divided into three parts, one part to be taken each day on an empty stomach.’”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi