I think its ayah 37 "wa idh taquulu lilladhee an3ama Allahu 3alayhi...."

And (remember) when you said to him (Zaid bin Harithah رضى the freedslave of the Prophet SAW) on whom Allah has bestowed Grace (by guiding him to Islam) and you (O Muhammad SAW too) have done favour (by manumitting him) "Keep your wife to yourself, and fear Allah." But you did hide in yourself (i.e. what Allah has already made known to you that He will give her to you in marriage) that which Allah will make manifest, you did fear the people (i.e., Muhammad SAW married the divorced wife of his manumitted slave) whereas Allah had a better right that you should fear Him. So when Zaid had accomplished his desire from her (i.e. divorced her), We gave her to you in marriage, so that (in future) there may be no difficulty to the believers in respect of (the marriage of) the wives of their adopted sons when the latter have no desire to keep them (i.e. they have divorced them). And Allah's Command must be fulfilled.

wassalaam