Translation:

11. Hast thou not observed the Hypocrites say to their misbelieving brethren among the People of the Book? "If ye are expelled We too will go out with you and we will never hearken to anyone in your affair; and if ye are attacked (in fight) we will help you." But Allah is witness that they are indeed liars.

Notes (Tafseer)

5386. The Jews of the Banu Nadhir had been assured by the Hypocrites of Madinah of their support to their cause. They had thought that their defection from the Prophet's Cause would so weaken that cause that they would save their friends. But they never intended to undertake any act involving self-sacrifice on their part; if they had helped their Jewish friends, it was not likely that they would have succeeded; and if they had actually gone to the fight; they had neither valour nor fervour to support them, and they would have fled ignominiously before the discipline, earnestness, and Faith of the men of Islam.

5387. For this actually happened. They never stirred a finger for the Jews, and they never intended to do so. And Allah knows all their motives and secrets: cf. xlvii. 26, n. 4850.