عَنْ اَبَانِ بْنِ تَغْلِبَ قَالَ قُلْتُ لِاَبِي عَبْدِ اللهِؑ مَنْ عَرَفَ الْاَئِمَّةَ وَ لَمْ يَعْرِفِ الْاِمَامَ الَّذِي فِي زَمَانِهِ اَ مُؤْمِنٌ هُوَ قَالَ لَا قُلْتُ اَ مُسْلِمٌ هُوَ قَالَ نَعَمْ
Abaan Ibn Taghlib (who was an extremely respected companion) chronicles, “I asked Imam Abu Abdillah al-Sadeq (peace be upon him), ‘Whoever recognizes the Imams (peace be upon them) but did not recognize the Imam who is in his time, is he a believer?’ He (peace be upon him) replied, ‘No’. I inquired, ‘Is he a Muslim?’ He (peace be upon him) answered, ‘Yes.’
Note:
Here, the word ‘Muslim’ is used in its second sense as in Surah Hujuraat (49): Verse 14 قالَتِ الْاَعْرابُ آمَنَّا قُلْ لَمْ تُؤْمِنُوا وَ لكِنْ قُولُوا اَسْلَمْنا وَ لَمَّا يَدْخُلِ الْإيمانُ في قُلُوبِكُمْ and not in its first sense i.e. that is, the one who has really brought Islam and believed in.
References:
1. Behaar al-Anwaar, vol. 23, p. 96, H. 2
2. Kamaal al-Deen, vol. 2, p. 410, H. 3