"I saw the Prophet - (a number of times) such that I was not able to count - using the Siwak while he was fasting."  

رَأَيْتُ النَّبِيَّ ﷺ مَا لاَ أُحْصِي يَتَسَوَّكُ وَهُوَ صَائِمٌ قَالَ وَفِي الْبَابِ عَنْ عَائِشَةَ