It is narrated with the previous chain that the Prophet Muhammad (peace be upon him) said: Do not fast one or two days before Ramadan, except for a person who has a habit of fasting, then he may fast. It is narrated with the previous chain that the Prophet Muhammad (peace be upon him) said: Begin fasting upon sighting the moon and celebrate Eid al-Fitr upon sighting the moon. If it is cloudy, then complete thirty days of fasting.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 9654