Amputating an Otiose Finger

You asked, O brother, about cutting off the extra finger if cutting it is not difficult and will not cause hardship.  This is not objectionable. Put your trust in Allah and cut it off.

– Shaykh Ahmad ibn Idris, The Letters of Shaykh Ahmad ibn Idris, p. 16

Note: This refers to polydactylism: to have a malformation where there is an extra finger.