Yahya related to me from Malik from Salama ibn Safwan ibn Salama az-Zuraqi that Zayd ibn Talha ibn Rukana, who attributed it to the Prophet, may Allah bless him and grant him peace, said, “The Messenger of Allah, may Allah bless him and grant him peace, said, ‘Every deen has an innate character. The character of Islam is modesty.’
Al-Muwatta – Hadith 47.2.9

Narrated Masruq: We were sitting with ‘Abdullah bin ‘Amr who was narrating to us (Hadith). He said, “Allah’s Apostle was neither a Fahish nor a Mutafahhish, and he used to say, ‘The best among you are the best in character (having good manners).’ ”
Sahih Al-Bukhari – Book 73 Hadith 61