Imām Saʿīd b. Al-Musayyib – Allāh have mercy on him – said:

The Sunnah of Al-Fiṭr consists of three things: Walking to the prayer place (muṣallā), eating before leaving [for the prayer] and taking a full bath.

Al-Firyābī, Aḥkām Al-ʿEidayn #18. Shaykh Al-Albānī graded its chain of transmission ṣaḥīḥ in Irwāʾ Al-Ghalīl 3:104.