Sayyiduna Abu Musa (may Allah be pleased with him) narrates that I once came to the Messenger of Allah (peace and blessings of Allah be upon him) and found him using a miswak with his hand, and a sound of "ugh" was coming from his mouth, and the miswak was in his mouth as if he were about to vomit.
Hadith Referenceاللؤلؤ والمرجان / كتاب الطهارة / 143
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 4 كتاب الوضوء: 73 باب السواك»
Brief Explanation
If the tooth-stick (miswak) is used deep inside the throat, this kind of sound is produced. This was the state of the Messenger of Allah (sallallahu alayhi wa sallam) at that time. What is meant by this is exaggeration (thoroughness) in using the tooth-stick (miswak). (Raaz)