The word(s) "backs" appears 19 time(s) in 19 verse(s) in Quran in Muhammad Pickthal translation.

(11) He said: O my people! Bethink you: if I am (acting) on a clear proof from my Lord and He sustaineth me with fair sustenance from Him (how can I concede aught to you)? I desire not to do behind your backs that which I ask you not to do. I desire naught save reform so far as I am able. My welfare is only in Allah. In Him I trust and unto Him I turn (repentant).

(12) So travel with thy household in a portion of the night, and follow thou their backs. Let none of you turn round, but go whither ye are commanded.

(13) And We place upon their hearts veils lest they should understand it, and in their ears a deafness; and when thou makest mention of thy Lord alone in the Qur'an, they turn their backs in aversion.

(14) If those who disbelieved but knew the time when they will not be able to drive off the fire from their faces and from their backs, and they will not be helped!

(15) And, by Allah, I shall circumvent your idols after ye have gone away and turned your backs.

(16) And verily they had already sworn unto Allah that they would not turn their backs (to the foe). An oath to Allah must be answered for.

(17) And they turned their backs and went away from him.

(18) That ye may mount upon their backs, and may remember your Lord's favour when ye mount thereon, and may say: Glorified be He Who hath subdued these unto us, and we were not capable (of subduing them);

(19) Then how (will it be with them) when the angels gather them, smiting their faces and their backs!