Surah Al-Ma'idah — Ayah 111 (5:111)
وَإِذۡ أَوۡحَيۡتُ إِلَى ٱلۡحَوَارِيِّـۧنَ أَنۡ ءَامِنُواْ بِي وَبِرَسُولِي قَالُوٓاْ ءَامَنَّا وَٱشۡهَدۡ بِأَنَّنَا مُسۡلِمُونَ ١١١
English translation (Saheeh International)
And [remember] when I inspired to the disciples, "Believe in Me and in My messenger [i.e., Jesus]." They said, "We have believed, so bear witness that indeed we are Muslims [in submission to Allāh]."
Brief commentary
Another favour that Allah reminded him about was that Allah created assistants for him when He inspired the disciples to have faith in Him and in Jesus. They submitted to that and responded saying, ‘I believe. Be a witness, O our Lord, that we submit to You in devotion’.