As regarding al-Shahristani who discusses those who dodged...

As regarding al-Shahristani who discusses those who dodged the draft in Usamah's army, narrating their story as a generally accepted fact, it has been narrated in one hadith documented by Abu Bakr Ahmad ibn ‘Abdul-Aziz al-Jawhari in his book Al-Saqifa , from which I quote here this much for you verbatim : "Ahmad ibn Ishaq ibn Salih has narrated a tradition to us from Ahmad ibn Siyar from Sa’d ibn Kathir al-Ansari whose men quote ‘Abdullah ibn ‘Abdul-Rahman saying that when the Messenger of Allah (pbuh) fell sick shortly before his death, he appointed Usamah ibn Zayd ibn Harithah to take charge in leading an army most of which were men from the Muhajirün and the Ansar.

Among them were: Abu Bakr, ‘Umar, Abu ‘Ubaydah ibn al-Jarrah, ‘Abdul-Rahmn ibn ‘Awf, Talhah, and al-Zubayr, and ordered him to invade Mu'ta, where his father Zayd had been murdered, and to invade the valley of Palestine. Usamah slackened, and so did the rest of the army, and the Messenger of Allah, peace be upon him and his progeny, though sick, kept emphasizing that the army must rush there, till Usamah said to him: ‘O Messenger of Allah!

Would you permit me to stay for a few days till Allah Almighty heals you?' He answered: ‘Go and proceed, supported by the blessings of Allah.' He said: ‘O Messenger of Allah!

If I proceed while you are sick like that, I will be going with a heart swollen with pain.' He (pbuh) said: ‘Proceed towards victory in good health.' Usamah persisted: ‘But I hate to keep asking the travellers about your condition.' He said: ‘Proceed to carry out my orders,' then he, peace be upon him and his progeny, fainted. Usamah left and prepared to proceed.

When the Messenger of Allah (pbuh) regained his consciousness, he immediately inquired about Usamah, and he was told that he and his men were preparing to proceed, whereupon he kept repeating: ‘Carry out Usamah's mission; the curse of Allah be upon whoever dodges its draft.' Usamah finally left the city, the flag above his head, surrounded by the companions, till he reached Jurf.

In his company were Abu Bakr, ‘Umar, and most of the Muhajirün and the Ansar such as Asid ibn Hadr, Bashir ibn Sa’d, and many other dignitaries. Then he received a messenger sent by Umm Ayman who informed him to go ahead and enter the city because the Prophet (pbuh) was dying. He immediately left for Medina with the standard still in his hand.