What is the nūn sākinah rule in «عَنْ صَلَاتِهِمْ»?

Al-Māʿūn and Al-Humazah: Applied Assimilation, Concealment, Madd and Hāʾ Rules

• Iqlāb
• Ikhfāʾ with ghunnah
• Throat iẓhār
• Non-nasal idghām