هُمَا يَتَفَاوَدَانِ العِلْمَ

(ISh, K) is a phrase used by the vulgar, (ISh,) but the correct expression is يَتَفَايَدَانِ, meaning They two impart knowledge, each to the other: (K:) or يتفايدان بَالْمَالِ بَيْنَهُمَا They two give, of the property, each to the other; or profit, or benefit, each other therewith: (ISh:) or, in the opinion of MF, each is allowable. (TA. [See also article فيد.])