The Messenger of Allah ﷺ used to brush his teeth with the siwak two or three times during the night. When he rose to pray at night, he would pray four units of prayer without speaking or giving any instruction, and he would say the closing salam between every two units.
حدثنا محمد بن عبيد حدثنا واصل عن أبي سورة
أن رسول الله ﷺ كان يستاك من الليل مرتين أو ثلاثا وإذا قام يصلي من الليل صلى أربع ركعات لا يتكلم ولا يأمر بشيء ويسلم بين كل ركعتين
No references are available.
Its chain is daif because of Wasil bin Saaib and Abu Sawrah, and Haythami declared it daif at 2/271 and 1/230, on account of Wasil alone. It is found in Tabarani's Al-Kabir 4/178, no. 4967.