If the seller and purchaser dispute over meat, and the purchaser says, “This meat has spoiled and become rancid,” while the seller says, “No,” then a man may testify, on the basis of smell, that it has spoiled.
An example of taste is where the purchaser says, “These dates are old and their taste has changed,” while the seller says, “No; rather, they are fresh dates whose taste has not changed.” A person may then testify regarding them on the basis of taste. Or the purchaser may say, “These grapes have not ripened, so they are sour,” while the seller says, “Rather, they are ripe and sweet.” By what means can this be known? By taste. Testimony based on touch is likewise permissible—for example, that something is dry or moist, soft or rough.
In any case, a person may testify only to what he knows through one of the five senses. The evidence for this is Allah’s saying: “Except for those who testify to the truth knowingly.” [al-Zukhruf 43:86] This is because testimony is a report concerning an actual matter, so he must know that actual matter. Testimony is purely a report; it is not a judicial ruling, such that we might say that rulings may be based on circumstantial evidence. As mentioned previously, judgment on the basis of circumstantial evidence is permissible, but testimony is purely a report, and a report is permissible only when the one reporting is certain that what he reports occurred, or that what he reports is true.
Is it a condition that the person against whom testimony is given know that a witness is present? This is not a condition. Thus, if the holder of a right brings the defendant to a place and arranges for someone to witness the matter while concealed, this is permissible. For if the person liable for the right is alone with its holder, he acknowledges it; but when someone else is present, he denies it. So the holder of the right employs a stratagem and invites him—for example—for coffee. When he arrives, he says to him, “Now that no one can see us, do you not remember when I lent you such-and-such, on such-and-such a day…”