Sayyidah Aishah Siddiqah (may Allah be pleased with her) narrates: The Prophet (peace and blessings be upon him) said: "The siwak is a cause of purifying the mouth and of the Lord's pleasure."
Imam Abu Ya'la recorded this report with two chains: one of them contains a narrator, Ibn Ishaq, who is thiqah (trustworthy) but a mudallis (one who conceals defects in the chain), while the narrators of the other chain are the narrators of the "Sahih".
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1116