The word(s) "unbelief" appears 17 time(s) in 16 verse(s) in Quran in Abdullah Yusuf Ali translation.

(11) Say to the Unbelievers, if (now) they desist (from unbelief), their past would be forgiven them; but if they persist, the punishment of those before them is already (a matter of warning for them).

(12) Verily the transposing (of a prohibited month) is an addition to unbelief: the Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, in order to adjust the number of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith.

(13) The Arabs of the desert are the worst in unbelief and hypocrisy, and most fitted to be in ignorance of the command which Allah hath sent down to His Messenger: But Allah is All-knowing, All-Wise.

(14) But those in whose hearts is a disease,- it will add doubt to their doubt, and they will die in a state of unbelief.

(15) Any one who, after accepting faith in Allah, utters unbelief,- except under compulsion, his heart remaining firm in Faith - but such as open their breast to unbelief, on them is Wrath from Allah, and theirs will be a dreadful Penalty.

(16) And know that among you is Allah's Messenger: were he, in many matters, to follow your (wishes), ye would certainly fall into misfortune: But Allah has endeared the Faith to you, and has made it beautiful in your hearts, and He has made hateful to you unbelief, wickedness, and rebellion: such indeed are those who walk in righteousness;-