Say, "I only advise you of one [thing] - that you stand for Allah, [seeking truth] in pairs and individually, and then give thought." There is not in your companion any madness. He is only a warner to you before a severe punishment.
Sahih International · EN
Dis: «Je vous exhorte seulement à une chose: que pour Allah vous vous leviez, par deux ou isolément, et qu'ensuite vous réfléchissiez. Votre compagnon (Muhammad) n'est nullement possédé: il n'est pour vous qu'un avertisseur annonçant un dur châtiment».
Muhammad Hamidullah · FR
Tafsir
Say - O Messenger, to these idolaters: “I only direct you to and advise you of one characteristic, which is that you stand free from desires, for Allah’s sake, in twos and individually, then think about the life of your companion and what you know of his intelligence, truthfulness and trustworthiness”, so that it becomes clear to you that he (peace be upon him) is not insane. He is not but a warner to you before a severe punishment, if you do not repent to Allah from associating partners with Him.
Al-Mukhtasar fi Tafsir al-Quran · Tafsir Center for Quranic StudiesRead Ibn Kathir (Ibn Kathir (abridged, English))
Say: "I exhort you to one (thing) only, that you stand up for Allah's sake in pairs and singly, and reflect, there is no madness in your companion. He is only a warner to you in face of a severe torment. (46)
Refutation of Their Accusation that the Prophet (صلی اللہ علیہ وسلم) was Insane
Allah says: 'Say, O Muhammad, to these disbelievers who claim that you are crazy,'
إِنَّمَا أَعِظُكُمْ بِوَاحِدَةٍ
(I exhort you to one (thing) only,) meaning, 'I am only telling you to one thing,' and that is:
أَنْ تَقُومُوا لِلَّهِ مَثْنَىٰ وَفُرَادَىٰ ثُمَّ تَتَفَكَّرُوا ۚ مَا بِصَاحِبِكُمْ مِنْ جِنَّةٍ ۚ
(that you stand up for Allah's sake in pairs and singly, and reflect, there is no madness in your companion.) meaning, 'stand sincerely before Allah, without being influenced by your own desires or tribal feelings, and ask one another, is Muhammad crazy? Advise one another,'
ثُمَّ تَتَفَكَّرُوا
(and reflect) means, let each person look within himself concerning the matter of Muhammad ﷺ, and ask other people about him if he is still confused, then let him think about the matter. Allah says:
أَنْ تَقُومُوا لِلَّهِ مَثْنَىٰ وَفُرَادَىٰ ثُمَّ تَتَفَكَّرُوا ۚ مَا بِصَاحِبِكُمْ مِنْ جِنَّةٍ ۚ
(that you stand up for Allah's sake in pairs and singly, and reflect, there is no madness in your companion.)
This meaning was stated by Mujahid, Muhammad bin Ka'b, As-Suddi, Qatadah and others. This is what is meant by the Ayah.
إِنْ هُوَ إِلَّا نَذِيرٌ لَكُمْ بَيْنَ يَدَيْ عَذَابٍ شَدِيدٍ
(He is only a warner to you in face of a severe torment.) Al-Bukhari recorded that Ibn 'Abbas, may Allah be pleased with him, commented on this Ayah: "One day, the Prophet ﷺ climbed up As-Safa' and shouted,
يَا صَبَاحَاهْ
(O people!) The Quraysh gathered around him, and said, 'What is the matter with you?' He said,
أَرَأَيْتُمْ لَوْ أَخْبَرْتُكُمْ أَنَّ الْعَدُوَّ يُصَبِّحُكُمْ أَوْ يُمَسِّيكُمْ أَمَا كُنْتُمْ تُصَدِّقُونِّي
(What do you think? If I told you that the enemy were approaching and will reach us in the morning or in the evening, would you believe me?) They said, 'Of course.' He ﷺ said:
فَإِنِّي نَذِيرٌ لَكُمْ بَيْنَ يَدَيْ عَذَابٍ شَدِيدٍ
(I am a warner to you in the face of a severe punishment.) Abu Lahab said, 'May you perish! You have called us together only to tell us this?' Then Allah revealed:
تَبَّتْ يَدَا أَبِي لَهَبٍ وَتَبَّ
(Perish the two hands of Abu Lahab and perish he!)(111:1) We have already discussed this in our Tafsir of the Ayah:
وَأَنْذِرْ عَشِيرَتَكَ الْأَقْرَبِينَ
(And warn your tribe of near kindred)(26:214).
Arabic text: Tanzil (Uthmani). Translations: Sahih International (en), Muhammad Hamidullah (fr). tanzil.net