Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Had they gone forth among you) with you (they had added to you naught save trouble) evil and corruption (and had hurried to and fro among you) they would have marched riding their camels in the middle of you, (seeking to cause sedition among you) seeking to cause evil, corruption, humiliation and damage; (and among you there are some who would have listened to them) among you there are spies for the disbelievers. (Allah is Aware of evil-doers) i.e. the hypocrites: 'Abdullah Ibn Ubayy and his hosts.
Had they gone forth among you, they would only have caused you more trouble, [more] corruption, by abandoning the believers, and would have hurried to and fro among you, that is, they would have hastened to spread slander among you, seeking, desiring, to stir up sedition, by casting enmity, between you; and among you there are some who would listen to them, to what they say, listening in readiness to accept it; and God knows the evildoers.
(And if they had intended to march out,), with you to participate in Jihad
لأَعَدُّواْ لَهُ عُدَّةً
(certainly, they would have made some preparation for it) they would have prepared for such task,
وَلَـكِن كَرِهَ اللَّهُ انبِعَاثَهُمْ
(but Allah was averse to their being sent forth) Allah hated that they should go with you,
(so He made them lag behind, and stay away from Jihad,
وَقِيلَ اقْعُدُواْ مَعَ الْقَـعِدِينَ
(and it was said (to them): "Sit you among those who sit (at home)'') as a part of what was decreed for them not that He legislated that they stay behind. Allah then explained why He disliked that they march with the believers, saying,
(and they would have hurried about in your midst sowing sedition among you) They would have rushed to spread false stories, hatred and discord among you,
وَفِيكُمْ سَمَّـعُونَ لَهُمْ
(and there are some among you who would have listened to them.) who would have obeyed them, given preference to their speech and words and asked them for advice, unaware of the true reality of these hypocrites. This might have caused corruption and great evil between the believers. Muhammad bin Ishaq said, "Those who sought permission (from the Messenger to lag behind) included some of the chiefs, such as `Abdullah bin Ubayy bin Salul and Al-Jadd bin Qays, who were masters of their people. Allah also made them lag behind because He knew that if they went along with the Messenger they would sow sedition in his army.'' There were some in the Prophet's army who liked these chiefs and were ready to obey them, because they considered them honorable,
وَفِيكُمْ سَمَّـعُونَ لَهُمْ
(and there are some among you who would have listened to them) 9:47. Allah next reminds of His perfect knowledge, saying,
وَاللَّهُ عَلِيمٌ بِالظَّـلِمينَ
(And Allah is the All-Knower of the wrongdoers.) Allah says that He knows what occurred, what will occur and if anything would have occurred, how it would occur, such as,
(And if We had ordered them (saying), "Kill yourselves (the innocent ones kill the guilty ones) or leave your homes,'' very few of them would have done it; but if they had done what they were told, it would have been better for them, and would have strengthened their conviction. And indeed We would then have bestowed upon them a great reward from Ourselves. And indeed We would have guided them to the straight way) 4:66-68.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
Allah held them back for He did not like that they should join Jihad unwillingly without any sincere intention for it. As they had no mind to make sacrifices to exalt the cause of Islam, and, therefore, would have taken part in it. half-heartedly to escape the taunts of the Muslims or to create mischief, this would have resulted in a greater evil, as has been stated explicitly in the next verse (48).
(Had it been a near adventure and an easy journey they had followed thee…) [9:42-47]. Allah then revealed about those hypocrites who stayed behind and did not take part in the Battle of Tabuk (Had it been a near adventure and an easy journey they had followed thee…). He also revealed (Had they gone forth among you they had added to you naught save trouble…). This is because when the Messenger of Allah, Allah bless him and give him peace, set forth, he camped his troops at al-Wada‘ ’s mountain trail while ‘Abd Allah ibn Ubayy camped his troops at a clear trodden path below the mountain trail of al-Wada‘. His troops were no less than the troops which were with the Prophet. When the Messenger of Allah, Allah bless him and give him peace, marched again, ‘Abd Allah ibn Ubayy, the hypocrites and the doubters stayed behind. To consol His Prophet, Allah bless him and give him peace, Allah, exalted is He, revealed (Had they gone forth among you they had added to you naught save trouble…).