Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) reports this saying of the Prophet (peace and blessings be upon him): "On grazing horses, one dinar is due for each horse."
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator al-Layth bin Hammad and a narrator Ghawrak, and both of them are da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزكاة / 4370