Responsa for Bava Metzia 114:10
יצאו קרקעות שאינן מטלטלין יצאו עבדים שהוקשו לקרקעות יצאו שטרות שאע"פ שמטלטלין אין גופן ממון הקדשות אמר קרא (שמות כב, ו) רעהו רעהו ולא הקדש:
R. papa said: This refers to bricks for building entrusted to the treasurer, in accordance with Samuel's dictum. For Samuel said: We build with unconsecrated material, and then consecrate it.<span class="x" onmousemove="('comment',' When building was necessary in the Temple, the materials were not bought with sacred funds, for this would immediately consecrate them, and the workmen by sitting on them would be trespassing. Therefore the materials were bought on credit, and paid for out of the Temple funds only when built up, whereby they became sanctified. Similarly, if one donated these building materials, he did not formally consecrate them until built in. Now, in reference to our discussion, the meaning is that the treasurer lent some of these unconsecrated materials for a higher return. No trespass is involved, since they were unconsecrated; on the other hand, since they were lent on behalf of hekdesh, the prohibition of usury does not apply. ');"><sup>10</sup></span>
Teshuvot Maharam
A. This is undoubtedly prohibited. But since the lending of charity-funds at a definite rate of interest became such a widespread custom throughout the Kingdom that the prohibition of the practice would not be heeded even if the law became known we refrain from publicising this prohibition. This opinion is expressed, however, in order to urge the compliance with this prohibition in the future (but R. Meir would express no opinion as to the necessity of repaying the interest already collected).
SOURCES: Pr. 73; L. 478. Cf. L 234; Cr. 101, 109; Tesh. Maim. Mishpatim, 14; R. Asher, Responsa 13, 8; Agudah B.M. 73.
Teshuvot Maharam
A. B should not give the ten quarter-marks to the poor of that community, since it would constitute unlawful usury. If, however, B earned profit with the ten marks, he must give part of the profit to the poor of another city, since one is not permitted to profit from charity money.
SOURCES: Pr. 999.