Abu Dawud said: What is correct is that this tradition is mursal (i.e. the link of the Companion is missing).
In-book : Book 15, Hadith 135
English translation : Book 14, Hadith 2605
15. Jihad (Kitab Al-Jihad)
باب فِيمَا يُسْتَحَبُّ مِنَ الْجُيُوشِ وَالرُّفَقَاءِ وَالسَّرَايَا