COMMENTARY on 4:81
A. Yusuf Ali:

Translation:
They have "Obedience" on their lips; but when they leave you, a section of them Meditate all night on things very different from what you tellest them. But Allah records their nightly (plots): So keep clear of them, and put your trust in Allah, and enough is Allah as a disposer of affairs. 600
Commentary:

600  If we trust people who are not true, they are more likely to hinder than to help. But Allah is All-Good as well as All-Powerful, and all our affairs are best entrusted to His care. He is the best Guardian of all interests. Therefore we should not trust the lip professions of hypocrites, but trust in Allah. Nor should our confidence in Allah be shaken by any secret plots that enemies hatch against us. We should take all human precautions against them, but having done so, we should put our trust in Allah, Who knows the inner working of events better than any human mind can conceive.

 

Muhammad Asad:

Translation:
And they say, "We do pay heed unto thee'' 95 - but when they leave thy presence, some of them devise, in the dark of night, [beliefs] other than thou art voicing; 96 and all the while God records what they thus devise in the dark of night. Leave them, then, alone, and place thy trust in God: for none is as worthy of trust as God.
Commentary:
95  Lit., "And they say, 'Obedience’" - a reference to the hypocrites of Medina, in the time of the Prophet, and - by implication - the hypocritical "admirers" and half-hearted followers of Islam at all times.
96  I.e., they surreptitiously try to corrupt the message of God's Apostle. The verb bata denotes "he spent the night"; in the form bayyata it signifies "he meditated by night [upon something, or upon doing something]", or "he devised (something) by night" (Lisan al-Arab), i.e., in secrecy, which is symbolized by "the dark of night".