A. Yusuf Ali:Translation:
(Respite will be granted) until, when the
messengers give up hope (of their people) and (come
to) think that they were treated as liars, 1795 there
reaches them Our help, and those whom We will are
delivered into safety. But never will be warded off our
punishment from those who are in sin.

Muhammad Asad:Translation:
[All the earlier apostles had to suffer persecution for a long time;] but at last 106 -when those apostles had lost all hope and saw themselves branded as liars 107 - Our succour attained to them: whereupon everyone whom We Milled [to be saved] was saved [and the deniers of the truth were destroyed]: for, never can Our punishment be averted from people who are lost in sin.
1795 Zannu (comes to think): I construe the nominative of this verb to be "the messengers" in agreement with the best authorities. Kudhibu is the usual reading, though Kudhdhibu, the alternative reading, also rests on good authority. I construe the meaning to be: that Allah gives plenty of rope to the wicked (as in Joseph's story) until His own Messengers feel almost that it will be hopeless to preach to them and come to consider themselves branded as liars by an unbelieving world; that the breaking-point is then reached; that Allah's help then comes swiftly to His men, and they are delivered from persecution and danger, while the wrath of Allah overtakes sinners, and nothing can then ward it off. This interpretation has good authority behind it, though there are differences of opinion.