From 'Abdallah ibn Hanzalah: The Prophet, peace be on him, said: "A dirham of riba which a man receives knowingly is worse than committing adultery thirty-six times" (Mishkat al-Masabih, Kittab al-Buyu', Bab al-riba, on the authority of Ahmad and Daraqutni).Bayhaqi has also reported the above hadith in Shu'ab al-iman with the addition that "Hell befits him whose flesh has been nourished by the unlawful" (ibid).
From 'Umar ibn al-Khattab: The last verse to be revelaed was on riba and the Prophet, peace be on him, was taken without explaining it to us; so give up not only riba but also ribah [whatever raises doubts in the mind about its rightfulness]. From Abu Sa'id al-khudri: The Prophet, peace be on him, said: "Gold for gold, silver for silver, wheat for wheat, barley for barley, dates for dates, and salt for salt - like for like, and hand-to-hand.
Whoever pays more or takes more has indulged in riba.
The taker and the giver are alike [in guilt]." (Muslim, ibid; and Musnad Ahmad).
From Abu Sa'id and Abu Hurayrah: A man employed by the Prophet, peace be on him, in Khaybar brought for him janib [dates of very fine quality].
According to some sources, ʿurf holds as much authority as 'ijma (consensus), and more than qiyas (legal reasoning by analogy). If it is in absolute opposition to Islamic texts, custom is disregarded.