מדרש על שמות 28:5

The masters said above: "No administrative body should consist of less than two." Whence is this inferred. R. Nachman said: "The passage reads (Ex. 28, 5) And they shall take the gold." Only because its administration requires two; but as to the honest}', one is sufficient; hence this is a support to R. Chanina, who said: "It happened once that Rabbi appointed two brothers as treasurers of the Kuppah." But, after all, what administration is there in collecting charity. It is as R. Nachman said in the name of Rabba b. Abahu: "One may take a pledge for charity even on Friday," [hence it is administration]. Is that so? Is it not written (Jer. 30, 20) I will punish all that oppress them; and R. Isaac b. Samuel b. Martha said in the name of Rab that it includes even the collector of charity. This presents no difficulty. One deals with a case in which the man is wealthy, and the other deals with a case in which the man is poor. As Raba pressed R. Nathan b. Ammi and took from him four hundred zuz for charity.