The Quran

101

وَمِمَّن حَولَكُم مِنَ الأَعرابِ مُنافِقونَ ۖ وَمِن أَهلِ المَدينَةِ ۖ مَرَدوا عَلَى النِّفاقِ لا تَعلَمُهُم ۖ نَحنُ نَعلَمُهُم ۚ سَنُعَذِّبُهُم مَرَّتَينِ ثُمَّ يُرَدّونَ إِلىٰ عَذابٍ عَظيمٍ

Muhammad Asad

But among the bedouin who dwell around you there are hypocrites; and among the people of the [Prophet's] City¹ [too] there are such as have grown insolent in [their] hypocrisy. Thou dost not [always] know them, [O Muhammad - but] We know them. We shall cause them to suffer doubly [in this world];² and then they will be given over to awesome suffering [in the life to come].

I.e., Medina. Originally, the city bore the name Yathrib; but after the exodus of the Prophet from Mecca it came to be known as Madinat an-Nabi ("the City of the Prophet") and, eventually, as Al-Madinah ("The City" par excellence).
I.e., first through failure in their worldly concerns, accompanied by pangs of conscience and the resulting spiritual distress, and then through a full realization, at the moment of dying, of the unforgivable nature of their sin (Manar XI, 19).