On the authority of Abu Muhammad al-Hasan ibn Ali ibn Abee Talib (may Allah be pleased with him), the grandson of the Messenger of Allah (peace and blessings of Allah be upon him), and the one much loved by him, who said:
I memorised from the Messenger of Allah (peace and blessings of Allah be upon him): "Leave that which makes you doubt for that which does not make you doubt."[At-Tirmidhi][An-Nasai]At-Tirmidhi said that it was a good and sound (hasan saheeh) hadeeth.
Reference: 40 Hadith Nawawi 11
English translation: Hadith 11