Abū Dāwūd (Dā’ūd) Sulaymān ibn al-Ash‘ath ibn Isḥāq al-Azdī al-Sijistānī, commonly known simply as Abū Dāwūd al-Sijistānī, was a scholar of prophetic hadith who compiled the third of the six "canonical" hadith collections recognized by Sunni Muslims, the Sunan Abu Dāwūd. He was a Persian speaker of Arab descent.
Many times I heard Imam Ahmad saying (when asked to give his opinion) on controversial scholarly issues 'I do not know.'
Prophet Muhammad (peace be upon him) said: By his good character a believer will attain the degree of one who prays during the night and fasts during the day.