What is the authenticity and interpretation of the Hadith stating that the Prophet, may Allah's prayers and peace be upon him, sent Sa'd ibn Zayd al-Ansari with captives from Banu Qurayza to Najd to exchange them for horses and weapons?

The biographers and chroniclers of military expeditions have circulated the report that the Messenger of Allah, peace and blessings be upon him, sent Sa'd ibn Zayd to Najd to sell the captives of Banu Qurayzah in order to buy horses and weapons. Its source is Ibn Ishaq, but its chain of transmission (sanad) is weak and broken, because Ibn Ishaq did not witness the event; he was from the followers of the Tabi'un. His narration is "mu'dal" (perplexing/problematic) because it is from a follower of the Tabi'in, which is weaker than a mursal narration (one where a Tabi'i narrates directly from the Prophet without mentioning the Companion). Despite the weakness of its chain, it is used as supportive evidence in works of biography and military expeditions, and it indicates the permissibility of selling disbelieving captives for a benefit, as Al-Shafi'i used it as proof for the permissibility of selling the captives of Banu Qurayzah to disbelievers, while observing the condition of not separating parents from their children, and not selling a child individually.