Narrated Jabir ibn Abdullah: The Messenger of Allah ﷺ used to keep to the rear when travelling and urge on the weak. He would take someone up behind him and make supplication for them all.
Hadith Referenceسنن ابي داود / كتاب الجهاد / 2639
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح, مشكوة المصابيح (3913), أخرجه الحاكم (2/115) أبو الزبير صرح بالسماع عنده
Benefits and Issues: The last and rear group of the army, in which generally weak, ill, and wounded (injured) people are present, is called the "saqah" (rear guard).
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 2639