Sincere

Sincere - genuine, meant truly or earnestly.

In the business world Sincerely yours or Yours Sincerely indicates that the person sending the correspondence (and the information and sentiments presented) are trustworthy.

Etymology

The triliteral root shīn kāf rā (ش ك ر), according to corpus.quran.com, occurs in the Quran 75 times.

In the Quran

(2:152) So remember Me that I may remember you, and be sincere (Arab. وَاشْكُرُوا, wa-ush'kurū) to Me and do not reject Me.

(2:172) O you who trust! But eat of that which We have given you, and be sincere (Arab. وَاشْكُرُوا, wa-ush'kurū) to Allah, if only you obey Him.