Ruling on delaying zakaah on trade goods due to lack of cash flow; does he have to borrow money in order to give zakaah?
Question

I have a bookshop in which I have trade goods that are equal to the nisaab (minimum threshold at which zakaah becomes due) and more, but I do not have cash with which to pay zakaah, and one full year has passed. My question is: Should I wait until I have sufficient money and then pay zakaah, or should I borrow money in order to pay zakaah?
Praise be to Allah.Firstly:
Zakaah is due on trade goods, when they reach the minimum threshold by themselves or when added to cash and other wealth, and one full Hijri year has passed.
You should work out their value when the year has passed, regardless of whether it is above or below the purchase price, and give one quarter of one tenth (2.5%).
Secondly:
If the wealth reached the minimum threshold and one full Hijri year has passed, then it becomes obligatory to give zakaah immediately, and it is not permissible to delay it unless one has an excuse.
An-Nawawi (may Allah have mercy on him) said: It is obligatory to give zakaah immediately when it becomes due, if one is able to pay, and it is not permissible to delay it. This was stated by Maalik, Ahmad and the majority of scholars, because Allah, may He be exalted, says (interpretation of the meaning): {and give zakah} [al-Baqarah 2:43], and the command means that it is to be done immediately.
End quote from Sharh al-Muhadhdhab (5/308).
In al-Iqna‘ ma‘a Sharhihi Kashshaaf al-Qinaa‘ (2/255) it says: It is not permissible to delay giving zakaah on wealth once it becomes due, if one is able to give it. So it must be given immediately… Unless the one for whom zakaah has become due fears harm, in which case he may delay it, because of the hadith: “There should be neither harm nor reciprocating harm.” … Or if the owner is poor and needs to keep his zakaah, and his own needs and livelihood will be affected if he gives it, and it can be taken from him when his situation improves. End quote.
See: al-Mughni (2/510).
Thirdly:
If you do not have sufficient cash to give zakaah on your trade goods, then you can give it in the form of the trade goods on which the zakaah is due, because the zakaah on trade goods may be given in the form of those goods, according to the more correct scholarly view. 
Imam Abu ‘Ubayd al-Qaasim ibn Salaam (may Allah have mercy on him) said:
If zakaah becomes due on a man’s trade goods, so he works out the amount of trade goods that he has and finds out that the zakaah reached the value of one garment, mount or slave, so he gives that particular item as the zakaah on his wealth, then in our view he has done well and his zakaah is acceptable. But if it is easier for him to pay the equivalent value in gold or silver, he may do that. This is how the zakaah on trade goods is to be given, in our view.
End quote from al-Amwaal by Abu ‘Ubayd (388); quoted from him by Humayd ibn Zanjawayh in al-Amwaal (3/974).
If the trade goods you have are of no benefit to the poor person who is entitled to zakaah, and he has no need of these trade goods, then there is nothing wrong with you delaying zakaah, in sha Allah, until you sell enough to cover the zakaah you have to give.
If you have sufficient cash to pay some of the zakaah, then you have to give what you can, and whatever you cannot give remains a debt that you owe until you are able to give it.
See also the answer to question no. 47761  .
And Allah knows best.