Abu Ishaq al-Khwarizmi, the judge of Khwarizm, narrates: I asked Asim al-Ahwal: Should a fasting person use the miswak? He said: Yes. I said: With both a fresh and a dry miswak? He said: Yes. I said: At the beginning of the day and at its end too? He said: Yes. I said: From whom is this narrated? He said: From Anas bin Malik (may Allah be pleased with him), from the Prophet (peace and blessings be upon him).
Only Abu Ishaq Ibrahim bin Baytar narrated this; he is also called Ibrahim bin Abd al-Rahman, the judge of Khwarizm. He narrated munkar (denounced) reports from Asim al-Ahwal in Balkh and is not used as evidence. It has also been narrated from him through another route that does not mention the beginning and end of the day.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8327