The Quran

وَإِذا سَمِعوا ما أُنزِلَ إِلَى الرَّسولِ تَرىٰ أَعيُنَهُم تَفيضُ مِنَ الدَّمعِ مِمّا عَرَفوا مِنَ الحَقِّ ۖ يَقولونَ رَبَّنا آمَنّا فَاكتُبنا مَعَ الشّاهِدينَ

Muhammad Asad

For, when they come to understand what has been bestowed from on high upon this Apostle, thou canst see their eyes overflow with tears, because they recognize something of its truth;¹ [and] they say: "O our Sustainer! We do believe; make us one, then, with all who bear witness to the truth.

Regarding this rendering of the phrase mimma 'arafu min al-haqq, see Zamakhshari and Razi; also Manar VII, 12. As for my translation of the expression idha sami'u as "when they come to understand", it is to be noted that beyond its primary significance of "he heard", the verb sami'a has often the meaning of "he understood" or "came to understand" (cf. Lane IV, 1427).