If you do not aid him [i.e., the Prophet (ﷺ)] - Allāh has already aided him when those who disbelieved had driven him out [of Makkah] as one of two,1 when they were in the cave and he [i.e., Muḥammad (ﷺ)] said to his companion, "Do not grieve; indeed Allāh is with us." And Allāh sent down His tranquility upon him and supported him with soldiers [i.e., angels] you did not see and made the word2 of those who disbelieved the lowest,3 while the word of Allāh4 - that is the highest. And Allāh is Exalted in Might and Wise.
Translation: Saheeh International (English)
1 The second was his companion, Abū Bakr.
2 i.e., their claims and slogans.
3 i.e., degraded and dishonored.
4 "Lā ilāha ill-Allāh" ("There is no deity except Allāh").
If you O believers, do not help the Messenger (peace be upon him) and respond to his call to strive for the sake of Allah, then Allah has already helped him when you were not with him; when the idolaters drove him away from Mecca with Abū Bakr aṣ-Ṣiddīq (may Allah be pleased with him), and the two of them hid in the cave of Thawr from the disbelievers who were chasing them. On that occasion, the Messenger of Allah (peace and blessings be upon him) told his companion Abū Bakr, who was scared that the idolaters would discover him, not to worry, because Allah was with them, supporting and helping them. Allah sent down His reassurance and tranquility upon the heart of His Messenger, and sent angels which they could not see to support them, making the word of the idolaters the lowest, and the word of Allah the highest by aiding His Religion. Allah is Mighty in His essence, power and force – nothing can overcome Him – and He Wise in His planning, decree and laws.