Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:20:109 –

That Day, no intercession will benefit except ˹that of˺ one to whom the Most Merciful has given permission and has accepted his word.  

On that day intercession will not profit, anyone, except ˹intercession˺ from him whom the Compassionate One permits, that he intercede for such ˹a person˺, and whose word He approves, that is to say, because such ˹an intercessor˺ will say, ‘there is no god but God’ (lā ilāha illā’Llāh).
القرآن:٢٠:١٠٩ –

يَوْمَئِذٍ لَا تَنْفَعُ الشَّفَاعَةُ إِلَّا مَنْ أَذِنَ لَهُ الرَّحْمَٰنُ وَرَضِيَ لَهُ قَوْلًا  

{يومئذ لا تنفع الشفاعة} أحداً {إلا من أذن له الرحمن} أن يشفع له {ورضي له قولا} بأن يقول: لا إله إلا الله.