Siwaak prescribed before every prayer
3-1-2018 | IslamWeb
Question:
Assalaamu alaykum wa rahmatullaahi wa barakaatuhu. Shaykh, I have a question about the Miswaak (tooth stick). I read a hadith that says that your prayer will be multiplied by 70 if you use a Miswaak before it. So my question regarding this is: if I pray two units of prayer of the Sunnah before the Fajr (or any prayer) and then two units of prayer of the Fajr, do I have to use the Miswaak before each of those two prayers, or is using it just before the two units of prayer of the Sunnah sufficient for the two units of the Fajr to be multiplied as well? Is there a certain time interval in which the Miswaak 70x multiplier needs to be renewed? May Allah reward you. Wassalaam.
Answer:
All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
The hadeeth that says that the prayer after using the Siwaak/Miswaak is better than the one without using it is not authentic, as we highlighted in fatwa 85904.
It is prescribed to use the Siwaak before every prayer. Abu Hurayrah, may Allah be pleased with him, narrated that the Prophet, sallallahu ‘alayhi wa sallam, said, "Were it not that I would be overburdening my community (or the people), I would have ordered them to use the Siwaak with every prayer." [Al-Bukhaari and Muslim]
Imaam An-Nawawi 
said, "If a person wants to perform a prayer concluded with Tasleem (the Salaam greeting) such as the Taraweeh prayer, Dhuha, four-unit-Sunnah-prayer of the Thuhr or ʻAsr, Tahajjud prayers, and the like, it is recommended to use the Siwaak before each two units of prayer because the Prophet, sallallahu ‘alayhi wa sallam, said, 'I would have ordered them to use the Siwaak before every prayer or with every prayer.'" [Al-Majmooʻ]
If you used the Siwaak for the Sunnah of the Fajr prayer, it is prescribed to use it again before the obligatory Fajr prayer. This applies to every prayer according to the wording of the hadeeth.
Allah knows best.