أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ سَعِيدٍ، عَنْ إِسْحَاقَ بْنِ سُلَيْمَانَ، عَنْ أَبِي سِنَانٍ، عَنْ أَبِي حُصَيْنٍ، عَنْ شَقِيقٍ، عَنْ حُذَيْفَةَ، قَالَ كُنَّا نُؤْمَرُ بِالسِّوَاكِ إِذَا قُمْنَا مِنَ اللَّيْلِ ‏.‏

It was narrated that Hudhaifah said: "We were commanded to use the siwak when we got up to pray at night." Translation Not Available

Book Ref: Sunan An Nisai Book 20 Hadith 1623
Web Ref:  Sunan An Nisai Vol 2 Book 20 Hadith 1624