Is it required to specify the length of the rental period, and what is the ruling on paying per click for advertisements?
Question

                A place on a webpage is specified for advertising for other websites. Is it a must or not to specify the period of time for renting this place, by saying: “I will put the advertisement on my website for one year”? Is it permissible to take the fees according to how many persons click on the advertisement, for example 1 SR per click?.
Praise be to Allah.
    There is nothing wrong with renting a space on a website for 
    advertisements for other sites, so long as those sites do not contain 
    anything haraam, such as websites for men and women to get to know one 
    another, or websites for haraam music and movies and plays, or immoral audio 
    and video links, or sites for followers of innovation, and so on. It is not 
    permissible to advertise for these, because that is taking part with them in 
    the haraam things that they are promoting. 

    Allaah says (interpretation of the meaning): 

    “Help you one another in Al‑Birr and At‑Taqwa (virtue, 
    righteousness and piety); but do not help one another in sin and 
    transgression. And fear Allaah. Verily, Allaah is Severe in punishment”

    [al-Maa’idah 5:2]

    It was narrated from Abu Hurayrah (may Allaah be pleased with 
    him) that the Messenger of Allaah  (peace and blessings of Allaah be 
    upon him) said: “Whoever calls others to guidance will have a reward like 
    that of those who follow it, without that detracting from their reward in 
    the slightest. And whoever calls others to misguidance will have a burden of 
    sin like that of those who follow it, without it detracting from their 
    burden in the slightest.” Narrated by Muslim (2674). 

     Seeking reward from Allaah for refraining from that which is 
    haraam, dubious or confused is something that points to strength and 
    certainty of faith, which bring glad tidings of a halaal provision, blessing 
    and great reward. 

    Secondly: 

    As for the length of the rental period, one of the conditions 
    of a rental contract being valid is that the period should be known, and the 
    rent should be known. 

    Ibn Qudaamah (may Allaah have mercy on him) said:  

    There is no difference of opinion among scholars concerning 
    the fact that it is permissible to rent property. Ibn al-Mundhir said: All 
    of the scholars from whom we acquired knowledge were unanimously agreed that 
    renting houses and animals is permissible.  

    But it is not permissible to rent it except for a specified 
    and known period. 

    Al-Mughni (5/260). 

    And he (may Allaah have mercy on him) said: 

    If renting is done for some amount of time, it must be known, 
    such as a month or a year. There is no difference of opinion concerning this 
    as far as we know. 

    Al-Mughni (5/251).  

    It is permissible, in a rental contract, to agree on a 
    certain amount of money every day, for example, or a certain amount of money 
    every month, without stipulating the end of the period. Ibn Qudaamah (may 
    Allaah have mercy on him) said in al-Mughni: If a person rents a 
    horse for the period of a campaign for one dirham every day, what is 
    narrated from Imam Ahmad is that (this contract) is valid, because ‘Ali (may 
    Allaah be pleased with him) hired himself out every day at a rate of one 
    date for every bucket, and the Ansaari did likewise, and the Prophet  
    (peace and blessings of Allaah be upon him) did not denounce that. End 
    quote. 

    Based on this, you may either stipulate in the contract a 
    complete period of time such as a month or a year for example, or you may 
    stipulate the rent for each day, for example, even if you do not stipulate 
    when the rental period will end. 

    Thirdly: 

    With regard to renting according to the number of clicks on 
    the ad, it seems that there is nothing wrong with it, so long as there is 
    agreement on the price per click, provided that you do not use a program to 
    increase the number of people entering the site or hire someone to enter the 
    site repeatedly.  

    This is akin to what was narrated about the Sahaabah, that 
    they worked to bring water, and were paid one date for each bucket. 

    It was narrated that Ka’b ibn ‘Ajrah said: I brought water 
    for a Jew, one date for each bucket, and I accumulated some dates, then I 
    brought them to the Prophet  (peace and blessings of Allaah be upon him) 
    … 

    Al-Haythami (may Allaah have mercy on him) said:  

    It was narrated by al-Tabaraani in al-Awsat and its 
    isnaad is jayyid. 

    Majmoo’ al-Zawaa’id wa Manba’ al-Fawaa’id 
    (11/230). 

    It was classed as hasan by al-Albaani in Saheeh 
    al-Targheeb wa’l-Tarheeb (3271). 

    The fact that the number of potential visitors is unknown at 
    the time when this rental contract is drawn up does not affect the validity 
    of the contract, because this uncertainty will eventually be resolved.  

    Based on that, if you rent this permissible website on a 
    monthly or annual basis for a fixed price, that is permissible, even if the 
    rental contract is based on the number of visitors to their site that is 
    advertised on your site, provided that the price per click is fixed, and so 
    long as another important condition is met, which is that you do not use a 
    program to increase the number of people entering the site or hire someone 
    to enter the site repeatedly, so as to increase your benefit from the site 
    that you are advertising. If you do that then you are sinning, and the money 
    that you get in return from that site is haraam to you, and you have to give 
    it back to them. 

    Many big companies have taken well-known international 
    websites to court and accused them of falsifying the numbers of visitors to 
    their ads. It says in the al-Jazeerah newspaper (issue no. 113, 
    Sunday 22 Rabee’ al-Awwal 1426 AH: 

    It was reported that distorting the figures for response to 
    ads on the basis of “payment per click” is regarded as a serious problem 
    faced by the information technology industry on the internet, because some 
    people –  including competitors or workers who have grudges against their 
    company – click more than once in a continual fashion on the ads, to 
    increase the size of the advertiser’s bill. This may cost the advertisers a 
    lot of money, and it is difficult to trace or stop the perpetrator. 

    The statistics of the non-profit Seembo foundation indicate 
    that between 36 and 58 per cent of advertisers feel very anxious about 
    distortion of the figures, but they cannot always catch the perpetrators. 
    End quote. 

    For more information please see the answer to question no. 
    98817. 

    And Allaah knows best.