Narrated Ibn Ishaq:Sahib maks means one who (receives) tithes (from) people.
حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الْقَطَّانُ، عَنِ ابْنِ مَغْرَاءَ، عَنِ ابْنِ إِسْحَاقَ، قَالَ الَّذِي يَعْشُرُ النَّاسَ يَعْنِي صَاحِبَ الْمَكْسِ .
AbuDaud
Tribute, Spoils, and Rulership (Kitab Al-Kharaj, Wal-Fai' Wal-Imarah) • Hadith 2938