Surah Yunus (Jonah), Verse 94

فَاِنْ كُنْتَ فِیْ شَكٍّ مِّمَّاۤ اَنْزَلْنَاۤ اِلَیْكَ فَسْـَٔلِ الَّذِیْنَ یَقْرَءُوْنَ الْكِتٰبَ مِنْ قَبْلِكَ لَقَدْ جَآءَكَ الْحَقُّ مِنْ رَّبِّكَ فَلَا تَكُوْنَنَّ مِنَ الْمُمْتَرِیْنَ ۟

Fa in kunta fee shakkin mimmaaa anzalnaaa ilaika fas'alil lazeena yaqra'oonal Kitaaba min qablik; laqad jaaa'akal haqqu mir Rabbika fa laa takoonanna minal mumtareen

“If thou wert in doubt as to what We have revealed unto thee, then ask those who have been reading the Book from before thee: the Truth hath indeed come to thee from thy Lord: so be in no wise of those in doubt.”

Quran 10:94 (Yusuf Ali Translation)