(By the snorting courses…) [100:1-11].
Muqatil said: “The Messenger of Allah, Allah bless him and give him peace, sent a military expedition to a clan of Banu Kinanah and appointed al-Mundhir ibn ‘Amr al-Ansari as its leader. When their news was late to come, the hypocrites said: ‘They have all been killed’, and so Allah, exalted is He, gave news about this expedition and revealed (By the snorting courses) meaning the horses of that expedition”.
‘Abd al-Ghafir ibn Muhammad al-Farisi informed us> Ahmad ibn Muhammad al-Basti> Muhammad ibn Makki> Ishaq ibn Ibrahim> Ahmad ibn ‘Abdah> Hafs ibn Jami‘> Simak> ‘Ikrimah> Ibn ‘Abbas who related that the Messenger of Allah, Allah bless him and give him peace, sent a cavalry in a mission but did not receive any news from them a month after they had left. And so it was revealed (By the snorting courses) i.e. the horses snorting with their nostrils.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou