养虎为患

yǎng hǔ wéi huàn

lit. to nurture a tiger invites calamity

fig. to indulge one's enemy is asking for trouble (idiom)

养

yǎng

to raise (animals)

虎

hǔ

tiger

为

wéi

variant of 為|为[wei2]

患

huàn

to suffer (from illness)