"The Prophet of Allah ﷺ would clean his teeth with the Siwak, then he would give me the Siwak in order to wash it. So I would first use it myself, then wash it and return it.
أَنَّهَا قَالَتْ كَانَ نَبِيُّ اللَّهِ ﷺ يَسْتَاكُ فَيُعْطِينِي السِّوَاكَ لأَغْسِلَهُ فَأَبْدَأُ بِهِ فَأَسْتَاكُ ثُمَّ أَغْسِلُهُ وَأَدْفَعُهُ إِلَيْهِ
"The Prophet of Allah ﷺ would clean his teeth with the Siwak, then he would give me the Siwak in order to wash it. So I would first use it myself, then wash it and return it. (Using translation from Abū Dāʾūd 52)
أَنَّهَا قَالَتْ كَانَ نَبِيُّ اللهِ ﷺ يَسْتَاكُ فَيُعْطِينِي السِّوَاكَ لِأَغْسِلَهُ فَابْدَأُ بِهِ فَأَسْتَاكُ ثُمَّ أَغْسِلُهُ وَأَدْفَعُهُ إِلَيْهِ