The word(s) "fruitless" appears 4 time(s) in 4 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) This day are (all) things good and pure made lawful unto you. The food of the People of the Book is lawful unto you and yours is lawful unto them. (Lawful unto you in marriage) are (not only) chaste women who are believers, but chaste women among the People of the Book, revealed before your time,- when ye give them their due dowers, and desire chastity, not lewdness, nor secret intrigues if any one rejects faith, fruitless is his work, and in the Hereafter he will be in the ranks of those who have lost (all spiritual good).

(2) As in the case of those before you: they were mightier than you in power, and more flourishing in wealth and children. They had their enjoyment of their portion: and ye have of yours, as did those before you; and ye indulge in idle talk as they did. They!- their work are fruitless in this world and in the Hereafter, and they will lose (all spiritual good).

(3) But it has already been revealed to thee,- as it was to those before thee,- "If thou wert to join (gods with Allah), truly fruitless will be thy work (in life), and thou wilt surely be in the ranks of those who lose (all spiritual good)".

(4) That is because they hate the Revelation of Allah; so He has made their deeds fruitless.