How sound is the narration regarding 'Umar ibn al-Khaṭṭāb's praise for 'Abd al-Raḥmān ibn Muljam and his sending him to teach people the Qur'an, as mentioned by al-'Asqalānī in (Lisān al-Mīzān)?

We have not come across any statement from scholars who authenticated or weakened this narration. However, Al-Sam'ani, Al-Safadi, Al-Dhahabi, and Al-Asqalani mentioned it using a صيغة التمريض (passive or unconfirmed form), such as Al-Sam'ani's statement: "And it was said: 'Umar ibn Al-Khattab wrote to Amr ibn Al-'As: 'Bring Abdurrahman ibn Muljam's house closer to the mosque so that people may learn the Qur'an and jurisprudence from him.' So, a place was expanded for him instead of his house." And 'Umar's praise of Abdurrahman ibn Muljam—if it were proven—was based on the circumstances apparent to him at the time, and the fitna of the Khawarij had not yet appeared.