When the children of a woman (in pre-Islamic days) did not survive, she took a vow on herself that if her child survives, she would convert it a Jew. When Banu an-Nadir were expelled (from Arabia), there were some children of the Ansar (Helpers) among them. They said: We shall not leave our children. So Allah the Exalted revealed; "Let there be no compulsion in religion. Truth stands out clear from error." Abu Dawud said: Muqlat means a woman whose children do not survive.  

كَانَتِ الْمَرْأَةُ تَكُونُ مِقْلاَتًا فَتَجْعَلُ عَلَى نَفْسِهَا إِنْ عَاشَ لَهَا وَلَدٌ أَنْ تُهَوِّدَهُ فَلَمَّا أُجْلِيَتْ بَنُو النَّضِيرِ كَانَ فِيهِمْ مِنْ أَبْنَاءِ الأَنْصَارِ فَقَالُوا لاَ نَدَعُ أَبْنَاءَنَا فَأَنْزَلَ اللَّهُ ﷻ { لاَ إِكْرَاهَ فِي الدِّينِ قَدْ تَبَيَّنَ الرُّشْدُ مِنَ الْغَىِّ }