"And when they come to you, they say, 'We believe,' while they have certainly entered with disbelief, and they have certainly left with it." Al-Kalbi said:
These are the hypocrites among the People of the Scripture. When they entered upon the Messenger of Allah, they would say, 'We believe,' while they had entered upon the Prophet as disbelievers, and they left his presence while they were [still] disbelievers, and they did not benefit at all from what they heard from him. They were among the Jews.
He said: "And Allah is most knowing of what they were concealing." They were concealing the religion of Judaism.
﴿وَإِذَا جَاءُوكُمْ قَالُوا آمَنَّا وَقَدْ دَخَلُوا بِالْكُفْرِ وَهُمْ قَدْ خَرَجُوا بِهِ﴾ قَالَ الْكَلْبِيُّ:
هَؤُلَاءِ مُنَافِقُو أَهْلِ الْكِتَابِ، كَانُوا إِذَا دَخَلُوا عَلَى رَسُولِ اللَّهِ، قَالُوا: آمَنَّا، وَقَدْ دَخَلُوا حِينَ دَخَلُوا عَلَى النَّبِيِّ كُفَّارًا، وَخَرَجُوا مِنْ عِنْدِهِ وَهُمْ كُفَّارٌ وَلَمْ يَنْتَفِعُوا بِمَا سَمِعُوا مِنْهُ بِشَيْءٍ؛ وَهُمْ مِنَ الْيَهُودِ.
قَالَ: ﴿وَاللَّهُ أَعْلَمُ بِمَا كَانُوا يكتمون﴾ كَانُوا يكتمون دين الْيَهُودِيَّة