Hadith on Siwak: Clean your mouth for the angels, the Quran

Ali reported: The Prophet, peace and blessings be upon him, said, “Verily, when the servant uses the toothstick and then stands to pray, an angel stands behind him and listens to his recitation. The angel draws near until his mouth coincides with his and nothing of the Quran comes out of it but that it enters the heart of the angel. Thus, purify your mouths for the Quran.

Source: Musnad al-Bazzār 568

Grade: Hasan (fair) according to Al-Albani

عَنْ عَلِيٍّ قَالَ قَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّ الْعَبْدَ إِذَا تَسَوَّكَ ثُمَّ قَامَ يُصَلِّي قَامَ الْمَلَكُ خَلْفَهُ فَتَسَمَّعَ لِقِرَاءَتِهِ فَيَدْنُو مِنْهُ حَتَّى يَضَعَ فَاهُ عَلَى فِيهِ فَمَا يَخْرُجُ مِنْ فِيهِ شَيْءٌ مِنَ الْقُرْآنِ إِلا صَارَ فِي جَوْفِ الْمَلَكِ فَطَهِّرُوا أَفْوَاهَكُمْ لِلْقُرْآنِ

568 البحر الزخار بمسند البزار

215 المحدث الألباني خلاصة حكم المحدث حسن في صحيح الترغيب