It was narrated from Sa'eed bin Jubair that Ibn 'Abbas said:
"For the one who makes unlawful is the swearing." (Sahih)And Ibn 'Abbas used to say: "You had the best example in the Messenger of Allah." (33:21) (DE)
English reference (DE): Vol. 3, Book 10, Hadith 2073 (DE)
Arabic reference (DE): Book 10, Hadith 2151 (DE)