A Sword
Satti Sutta (SN 1:21)

As she was standing there, the devatā recited this verse in the Blessed One’s presence:

“As if struck by a sword,
as if his head were on fire,
a monk should live the wandering life
	—mindful—
for the abandoning of sensual passion.”

The Buddha:

“As if struck by a sword,
as if his head were on fire,
a monk should live the wandering life
	—mindful—
for the abandoning of self-identity.”