´It was narrated that Abu Musa said:` "I came to the Messenger of Allah (ﷺ) when he was using the Siwak, and the end of the Siwak was on his toungue, and he was saying, "'A','a'."
Hadith Referenceسنن نسائي / كتاب الطهارة / 3
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:متفق عليه