Sorry, this is incorrect.
The correct answer is : Both verbal declaration and sincere belief in the heart are required
Ref: Surah Ai-Hujurat 49:14
Arabic:-
۞ قَالَتِ ٱلْأَعْرَابُ ءَامَنَّا ۖ قُل لَّمْ تُؤْمِنُوا۟ وَلَـٰكِن قُولُوٓا۟ أَسْلَمْنَا وَلَمَّا يَدْخُلِ ٱلْإِيمَـٰنُ فِى قُلُوبِكُمْ ۖ وَإِن تُطِيعُوا۟ ٱللَّهَ وَرَسُولَهُۥ لَا يَلِتْكُم مِّنْ أَعْمَـٰلِكُمْ شَيْـًٔا ۚ إِنَّ ٱللَّهَ غَفُورٌۭ رَّحِيمٌ ١٤
Translation:
˹Some of˺ the nomadic Arabs say, “We believe.” Say, ˹O Prophet,˺ “You have not believed. But say, ‘We have submitted,’ for faith has not yet entered your hearts.1 But if you obey Allah and His Messenger ˹wholeheartedly˺, He will not discount anything from ˹the reward of˺ your deeds. Allah is truly All-Forgiving, Most Merciful.”
Tafseer / Explanation:
1. Some desert Arabs claimed to have true faith (iman), but Allah corrected them by saying they had only submitted outwardly (Islam), not inwardly.
2. True faith resides in the heart and includes sincere belief and conviction beyond verbal declaration.
3. Allah reminds them that faith becomes complete only when it enters the heart genuinely.
4. Their initial acceptance of Islam is acknowledged, but it is not yet full belief.
5. This verse teaches the distinction between outward submission (Islam) and inner faith (iman).