were of the opinion that riba in the Qur'an was an ambiguous (mujmal) term, the meaning of which was not clear per se, and therefore the ambiguity had to be cleared by the Tradition" (another name for ahadith). Different sources report different types and numbers of riba-related ahadith. According to Farhad Nomani, there are "three principal types" of ahadith that deal with riba. The "most accepted or reliable sayings", found in most compilations of ahadith, that state that riba exists when "six articles of the same kind are either bartered unequally or not delivered immediately". (see Riba al-Fadl) Another set cite Ibn ʿAbbas, and report that there is "no riba except in deferment ... in delivery and/or payment". A third set quote Muhammad's "sermon on the occasion of the last pilgrimage," where he is reported to have said: "God has forbidden you to take riba, therefore all riba obligation shall henceforth be waived. Your capital, however, is yours to keep. You will neither inflict nor suffer inequity. God has judged that there shall be no riba and that all the riba due to `Abbas ibn `Abd al Muttalib shall henceforth be waived." Similarly, M.A. Khan states "there are three sets of Traditions relating to riba", including the riba al-fadl and last pilgriamge sermon. Another source, Abdulkader Thomas, states that "there are six authenticated ahadith that allow us to define" riba. And under "riba in hadith", Shariq Nisar of Global Islamic Finance, lists seven "general" ahadith and another six on "Riba al-Nasi'ah". Several narrators including Jabir, Abdul Rahman ibn Abdullah ibn Masoud, say that Muhammad cursed the accepter of usury and its payer, and one who records it, and the two witnesses, saying: They are all equal. Questions On the other hand, the ambiguity and lack of clarity of what constitutes riba is reported to been indicated by Caliph ʿUmar, who included it among the three concepts that "it would have been dearer to me than the world" had Muhammad "explained them clearly" (see above), and twentieth century Islamic scholar, Fazlur Rahman Malik, who sums up his analysis of the ahadith on riba saying: "In short, no attempt to define riba in the light of Hadith has been so far successful". According to Farhad Nomani, "it is known that Ibn `Abas", a companion of Muhammad, "was of the opinion that the only forbidden riba was the pre-Islamic riba." Nomani state that