Hadith: I came to the Prophet (may Allah's peace and blessings be upon him) while he was cleansing his mouth with a ripe tooth-stick. The edge of the tooth-stick was on his tongue and he was making a sound like: “ugh, ugh” as if he was heaving, and the tooth-stick was in his mouth

عن أبي موسى الأشعري رضي الله عنه قال: ((أتَيتُ النبي صلى الله عليه وسلم وهو يَسْتَاكُ بِسِوَاك رَطْب، قال: وطَرَفُ السِّوَاك على لسانه، وهو يقول: أُعْ، أُعْ، والسِّوَاك في فِيه، كأنَّه يَتَهَوَّع)).
[صحيح] - [متفق عليه. ملحوظة: لفظه أخذ من الجمع بين الصحيحين للحميدي]

Abu Mūsa al-Ash‘ari (may Allah be pleased with him) reported: I came to the Prophet (may Allah's peace and blessings be upon him) while he was cleansing his mouth with a ripe tooth-stick. The edge of the tooth-stick was on his tongue and he was making a sound like: "c2">“ugh, ugh” as if he was heaving, and the tooth-stick was in his mouth.”
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

Abu Mūsa al-Ash‘ari (may Allah be pleased with him) relates in this Hadīth that he came to the Prophet (may Allah's peace and blessings be upon him) while he was cleaning his mouth with a ripe tooth-stick – a ripe tooth-stick cleans better and does not crumble inside one's mouth and hurt. He was placing the tooth-stick on his tongue and was cleaning his mouth thoroughly, as if he was going to vomit.