From which verb is fa-sullī formed and what does it mean?

Imruʾ al-Qays: Address to Fāṭimah, Parting, and the Arrows of the Eyes (Verses 19–22)

• Salla, yasullu; to pull out or draw away
• Dharafa, yadhrifu; to shed tears
• Azmaʿa, yuzmiʿu; to resolve
• Ajmala, yujmilu; to act graciously