The tenants do not pay him rent because they are poor – how can he pay zakaah?
Question

                I have some properties that I rent out in Palestine, but the tenants are not paying me rent for the third year in a row, because they do not have enough work to help them buy their daily food, because of the tragic circumstances we are going through, such as curfews and closures. 

 I also have a house that is empty and is not rented out. Do I have to pay zakaah on these properties even though there is no fixed income from them? Or is it possible to delay paying zakaah until a time when circumstances improve and I am able to get the rent from the tenants?.
Praise be to Allah.We ask Allaah to grant victory to our brothers in Palestine 
      and elsewhere over their enemies, and to grant them divine support and 
      make them strong in the land. 
Patience, O people of Palestine; patience, O weak and 
    oppressed; for the support of Allaah will undoubtedly come. “Victory comes 
    with patience.” Saheeh al-Jaami’, 6806 
No matter how long the night, day must inevitably come, and 
    the light of dawn must inevitably dispel the darkness of night. 
Secondly: 
No zakaah is due on real estate, whether it is land, houses 
    or shops, etc, unless it is for trading, in the sense that one buys it in 
    order to trade in it by selling it and making a profit. 
So no zakaah is due on property which the owner rents out, 
    rather zakaah is due on the rent if it reaches the nisaab and one full hijri 
    year has passed. 
This nisaab is the equivalent of 85 grams of gold or 595 
    grams of silver. 
See question no. 2795. 
If the rent that you are owed by the tenants reaches the 
    value of the nisaab in gold or silver, and one hijri year has passed from 
    the time when it reached the nisaab, then the scholars differ as to whether 
    zakaah is due on the debt owed by one who is in difficulty. There are 
    several opinions: 
1 – That zakaah is not due in this case.  
This is the view of Qataadah, Ishaaq, Abu Thawr and the 
    people of Iraq, and was narrated from Ahmad and Ibn Hazm, because the person 
    is not able to benefit from (the property). 
Al-Muhalla, question no. 696; 
    al-Insaaf, 3/18 
2 – That he should pay zakaah for the years that have passed 
    when he receives the rent.  
This is the view of al-Thawri, Abu ‘Ubayd and the correct 
    view of the Shaafa’i and Hanbali madhhabs. Among the evidence they quote for 
    that is the saheeh report from ‘Ali (may Allaah be pleased with him) 
    concerning the debt that is not certain to be repaid. He said: “If he is 
    sincere, let him pay zakaah on it when he receives it, for whatever years 
    have passed.” Narrated by ‘Abd al-Razzaaq in al-Musannaf, 7116. 
And because it is 
    property that is under his control, so he must pay zakaah for the time that 
    has passed, like he pays zakaah for a debt that a rich man owes him.  
See al-Majmoo’ by al-Nawawi, 6/16; al-Mughni, 
    2/345; al-Insaaf by al-Mardaawi, 3/22 
3 – He should pay zakaah for one year when he gets it.  
This is the view of ‘Umar ibn ‘Abd al-‘Azeez, al-Hasan, 
    al-Layth and al-Awzaa’i, and is the view of Maalik as stated in 
    al-Muwatta’, 1/253, where he says: “With regard to debt the indisputable 
    view among us is that a person should not pay zakaah on it until he receives 
    it, even if it stayed with the debtor for several years, then he receives it 
    after that, he only has to pay zakaah on it for one year.”  
See al-Kaafi by Ibn ‘Abd al-Barr, 1/93 
This third view is the 
    one on which a fatwa from the Standing Committee for Issuing Fatwas (9/190) 
    is based, in which it says: 
If the debt is owed by someone who is not well off, then he 
    should pay zakaah for one year when he takes possession of it, even if more 
    than one year has passed. This was narrated from Imam Ahmad, and is the view 
    of Maalik. Shaykh ‘Abd al-Rahmaan ibn Hasan stated this in a fatwa and said: 
    This is the view favoured by Muhammad ibn ‘Abd al-Wahhaab (may Allaah have 
    mercy on him). 
It was also regarded as more likely to be correct by Shaykh 
    Ibn ‘Uthaymeen, who said that he should not pay zakaah on it until he takes 
    possession of it, and that when he does take possession of it, he should pay 
    zakaah for one year only. He said: If that debt is owed by one who is in 
    difficulty, then the correct view is that zakaah is not required, because 
    the owner has no right to demand his money according to sharee’ah, because 
    Allaah says (interpretation of the meaning): 
“And if the debtor is in a hard time (has no money), then 
    grant him time till it is easy for him to repay; but if you remit it by way 
    of charity, that is better for you if you did but know”
[al-Baqarah 2:280]
He is indeed not in 
    control of that money, so he does not have to pay zakaah on it. But if he 
    takes possession of it, then he must pay zakaah for one year only, even if 
    it remains in the possession of the debtor for ten years, because this is 
    like paying zakaah on things that come out of the earth when one acquires 
    them. Some of the scholars said that he should not pay zakaah for what is in 
    the past, rather he should start counting the year from scratch. But what we 
    have mentioned above is more on the safe side and is more likely to 
    discharge one's duty; he should pay zakaah for one year and then pay zakaah 
    after another year passes with it still in his possession. This is easy; it 
    is not difficult for a person to pay one quarter of one-tenth of a debt that 
    has been paid back to him after he had given up on it. This is a way of 
    showing gratitude to Allaah for having gotten it. 
Majmoo’ Fataawa wa Rasaa’il Ibn ‘Uthaymeen, 
    18/28 
In conclusion: no zakaah is due on these properties that you 
    have, either those that you are renting out or those that are empty. Rather 
    zakaah is due on the rent if it reaches the nisaab and one hijri year has 
    passed. If the rent that you are owed by these tenants reaches the nisaab, 
    then you should pay zakaah on it, when you receive it, for one year only, 
    even if a number of years has passed. 
And Allaah knows best.