The word(s) "truthful" appears 45 time(s) in 44 verse(s) in Quran in Muhammad Pickthal translation.

(11) Say: Can ye see yourselves, if the punishment of Allah come upon you or the Hour come upon you, (calling upon other than Allah)? Do ye then call (for help) to any other than Allah? (Answer that) if ye are truthful.

(12) Eight pairs: Of the sheep twain, and of the goats twain. Say: Hath He forbidden the two males or the two females, or that which the wombs of the two females contain? Expound to me (the case) with knowledge, if ye are truthful.

(13) Unto those who are Jews We forbade every animal with claws. And of the oxen and the sheep forbade We unto them the fat thereof save that upon the backs or the entrails, or that which is mixed with the bone. That we awarded them for their rebellion. And lo! we verily are truthful.

(14) They said: Hast come unto us that we should serve Allah alone, and forsake what our fathers worshipped? Then bring upon us that wherewith thou threatenest us if thou art of the truthful!

(15) Lo! those on whom ye call beside Allah are slaves like unto you. Call on them now, and let them answer you, if ye are truthful!

(16) O ye who believe! Be careful of your duty to Allah, and be with the truthful.

(17) Or say they: He hath invented it? Say: Then bring a surah like unto it, and call (for help) on all ye can besides Allah, if ye are truthful.

(18) And they say: When will this promise be fulfilled, if ye are truthful?

(19) Or they say: He hath invented it. Say: Then bring ten surahs, the like thereof, invented, and call on everyone ye can beside Allah, if ye are truthful!

(20) They said: O Noah! Thou hast disputed with us and multiplied disputation with us; now bring upon us that wherewith thou threatenest us, if thou art of the truthful.