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

(1) (They are) distracted in mind even in the midst of it,- being (sincerely) for neither one group nor for another whom Allah leaves straying,- never wilt thou find for him the way.

(2) He it is Who enableth you to traverse through land and sea; so that ye even board ships;- they sail with them with a favourable wind, and they rejoice thereat; then comes a stormy wind and the waves come to them from all sides, and they think they are being overwhelmed: they cry unto Allah, sincerely offering (their) duty unto Him saying, "If thou dost deliver us from this, we shall truly show our gratitude!"

(3) And we ordained that he refused suck at first, until (His sister came up and) said: "Shall I point out to you the people of a house that will nourish and bring him up for you and be sincerely attached to him?"...

(4) Now, if they embark on a boat, they call on Allah, making their devotion sincerely (and exclusively) to Him; but when He has delivered them safely to (dry) land, behold, they give a share (of their worship to others)!-