Ubaydullah bin Humayd (may Allah have mercy on him) said: I heard Imam al-Sha'bi (may Allah have mercy on him) say: Whoever abandons his animal because of sickness, it belongs to the one who treated it and restored it to health. Ubaydullah (may Allah have mercy on him) said: I said: O Abu Amr! From whom is this reported? He said: If you wish, I will count them out for you from the Companions of the Messenger of Allah (peace and blessings be upon him).
There is disagreement over whether this hadith is marfu' (attributed to the Prophet), and as a report from the Prophet (peace and blessings be upon him) it is munqati' (its chain is broken).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12115