Via his student akh Abu Nusaybah (Al-Balagah)
Text:
Our Shaykh Ahmed Musa Jibril (hafiẓahullah) gave nasheeha for those who have recently left misguidance and have adopted the haqq in-shaa-allah, he said:
"When someone has just been newly guided from kufr or from bid'ah to the haqq, then they need to sit in the back seat for quite some time, not to rush to engage in da'wah or be in public positions immediately, rather they need to focus on the tawbah between them and Allah Ta'alaa for their previous misguidance, and they need to concentrate on seeking knowledge to clear the residue of their old misguidance from their heads, and they need to focus on stabilizing their beliefs before putting themselves in the public forefront overnight.
It is known that when Abu Bakr as-Siddiq and 'Umar ibn al-Khattab (رضي الله عنهما) fought against murtadeen (apostates), and they would return to Islam, they (Abu Bakr and 'Umar) refused to allow those who had returned from riddah to ride horses or carry weapons until their repentance had become manifest.
In fact 'Umar wrote to his wali (governor) in Iraq, Sa'd ibn Abi Waqqās, and said, 'Do not use any of them (i.e., those who returned from riddah) in any positions, and do not seek their advice on matters of war.'"