The slave is a guardian of the property of his master.

Narrated 'Abdullah bin 'Umar:

That he heard Allah's Apostle saying, "Everyone of you is a guardian and is responsible for his charge;
the ruler is a guardian and is responsible for his subjects;
the man is a guardian in his family and responsible for his charges;
a woman is a guardian of her husband's house and responsible for her charges;
and the servant is a guardian of his master's property and is responsible for his charge." I definitely heard the above from the Prophet and think that the Prophet also said, "A man is a guardian of his father's property and responsible for his charges;
so everyone of you is a guardian and responsible for his charges."

حَدَّثَنَا أَبُو الْيَمَانِ، أَخْبَرَنَا شُعَيْبٌ، عَنِ الزُّهْرِيِّ، قَالَ أَخْبَرَنِي سَالِمُ بْنُ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ يَقُولُ " كُلُّكُمْ رَاعٍ وَمَسْئُولٌ عَنْ رَعِيَّتِهِ، فَالإِمَامُ رَاعٍ وَمَسْئُولٌ عَنْ رَعِيَّتِهِ، وَالرَّجُلُ فِي أَهْلِهِ رَاعٍ وَهْوَ مَسْئُولٌ عَنْ رَعِيَّتِهِ، وَالْمَرْأَةُ فِي بَيْتِ زَوْجِهَا رَاعِيَةٌ وَهْىَ مَسْئُولَةٌ عَنْ رَعِيَّتِهَا، وَالْخَادِمُ فِي مَالِ سَيِّدِهِ رَاعٍ وَهْوَ مَسْئُولٌ عَنْ رَعِيَّتِهِ ". قَالَ فَسَمِعْتُ هَؤُلاَءِ مِنَ النَّبِيِّ ﷺ وَأَحْسِبُ النَّبِيَّ ﷺ قَالَ " وَالرَّجُلُ فِي مَالِ أَبِيهِ رَاعٍ وَمَسْئُولٌ عَنْ رَعِيَّتِهِ، فَكُلُّكُمْ رَاعٍ وَكُلُّكُمْ مَسْئُولٌ عَنْ رَعِيَّتِهِ ".