It was the practice of the Prophet (peace and blessings be upon him):
"He (peace and blessings be upon him) would pray at night two rak'ahs at a time, then after concluding with salam he would use the tooth-stick (miswak)."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4961
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[حم ن هـ ك] عن ابن عباس. صحيح الترغيب ٢٠٨.