Al-Kāfi

Hadith 1138
food-drinketiquetteimam-aliahl-al-bayt
عَلِيُّ بْنُ مُحَمَّدٍ رَفَعَهُ قَالَ كَانَ أَمِيرُ الْمُؤْمِنِينَ ( عليه السلام ) يَسْتَاكُ عَرْضاً وَ يَأْكُلُ هَرْتاً وَ قَالَ الْهَرْتُ أَنْ يَأْكُلَ بِأَصَابِعِهِ جَمِيعاً .
5. Ali ibn Muhammad in a marfu‘ manner has said the following: “’Amir al-Mu’minin (a.s.), would brush his teeth widthwise and eat using all of his fingers.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī