Sunan of Abu Dawood Book 20, Hadith 2993

حَدَّثَنَا مَحْمُودُ بْنُ خَالِدٍ السُّلَمِيُّ، حَدَّثَنَا عُمَرُ، - يَعْنِي ابْنَ عَبْدِ الْوَاحِدِ - عَنْ سَعِيدٍ، - يَعْنِي ابْنَ بَشِيرٍ - عَنْ قَتَادَةَ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا غَزَا كَانَ لَهُ سَهْمٌ صَافٍ يَأْخُذُهُ مِنْ حَيْثُ شَاءَهُ فَكَانَتْ صَفِيَّةُ مِنْ ذَلِكَ السَّهْمِ وَكَانَ إِذَا لَمْ يَغْزُ بِنَفْسِهِ ضُرِبَ لَهُ بِسَهْمِهِ وَلَمْ يُخَيَّرْ ‏.‏

Qatadah said "When the Apostle of Allaah(ﷺ) participated in battle there was for him a special portion which he took from where he desired. Safiyyah was from that portion. But when he did not participate himself in his battle, a portion was taken out for him, but he had no choice."