Sa'id bin al-Musayyib (may Allah have mercy on him) narrates from Abd al-Rahman bin Uthman (may Allah be pleased with him), a man of Banu Taym, that they mentioned the frog before the Messenger of Allah (peace and blessings be upon him) as a medicine, and he (peace and blessings be upon him) "forbade killing it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19379