This du'a / supplication is for those seeking a marriage partner. Also to conceive a child. ( ... its like this, to be married legally to have a child.)
رَبِّ لَا تَذَرْنِي فَرْدًا وَأَنتَ خَيْرُ الْوَارِثِينَ
89 : سورة الأنبياء
"My Lord, do not leave me alone [with no heir], while you are the best of inheritors."
