If the imam forgets some verses, how can he recite them so that he will have completed the Qur'aan?
Question

                If the imam forgets a verse or something of Qur'aan during Taraaweeh prayers, then he remembers it later on, what should he do? Can he have completed the Qur'aan in the prayer even though he did not recite this verse?.
Praise be to Allah.
      The reader will not attain the reward for 
      completing the Holy Qur'aan unless he has recited all of it and not 
      omitted any part of it. If he omits a verse and does not recite it, then 
      he has not completed the Holy Qur'aan. 

    The scholars even said that he should recite 
    the Basmalah at the beginning of every soorah except Soorat Baraa’ah (al-Tawbah), 
    and he should pay attention to that so that he will have completed the 
    Qur'aan. 

    Al-Nawawi (may Allah have mercy on him) 
    said: 

    He should always recite Bismillaah al-Rahmaan 
    al-Raheem at the beginning of every soorah except Baraa’ah, as most of the 
    scholars said that it is a verse, as it is written in the Mushaf and it is 
    written at the beginning of all soorahs except Bara’aah. If he recites it 
    then he has definitely completed the recitation, and if he omits the 
    Basmalah he has omitted part of the Qur'aan according to the majority. End 
    quote. 

    Al-Tibyaan, 
    p. 61, 62 

    Based on that, it is essential for the 
    reader to recite what he forgot of the verses, so that he may attain the 
    reward for completing the Qur'aan. 

    The scholars (may Allah have mercy on them) 
    mentioned two ways narrated from the Salaf (early generation) of reciting 
    the verse or verses that the imam forgot during Taraweeh prayers: 

    1.He should put all 
    these verses together and recite them all on the last night of Ramadan. This 
    is what the imams used to do in Makkah in the past.

    2.When he remembers 
    the verse that he forgot, he should recite it [this applies if he is still 
    reciting in the prayer] and then resume his recitation until he has 
    finished. This was narrated from ‘Ali (may Allah be pleased with him).

    Shaykh al-Islam Ibn Taymiyah (may Allah have 
    mercy on him) said, noting that the order in which it is prescribed to 
    recite is waived in the case of forgetting: 

    … if he forgets some of the verses of the 
    soorah when praying qiyaam in Ramadan (i.e., Taraaweeh), he should not 
    repeat it [the entire soorah] or repeat what comes after it, but if he 
    deliberately changes the order of the verses in the soorah and recites the 
    later ones before the earlier ones, that is not permissible according to 
    scholarly consensus. 

    Imam Ahmad (may Allah have mercy on him) was 
    asked about the imam during the month of Ramadan omitting some verses from 
    the soorah: did he think that the one who was praying behind him should 
    recite them? 

    He said: Yes, he should do that. In Makkah 
    they used to appoint a man to write down what the imam forgot of verses and 
    so on, then on night of completion he would recite what he had omitted. 

    His companions -- such as Abu Muhammad (Ibn 
    Qudaamah) -- said: Rather that is mustahabb in order to complete the Qur'aan 
    and so as to attain a complete reward. The people of Makkah and Ahmad and 
    his companions thought that if the one who had omitted some verses recited 
    them later on when he remembered them, that was sufficient to be regarded as 
    having completed the Qur’aan and to attain the reward, even if that meant 
    the order of verses was not followed in this instance, because without 
    reciting these verses, his recitation of the soorah could not be regarded as 
    complete. This was narrated from ‘Ali: he forgot a verse from a soorah, then 
    whilst he was still reciting he recited it, then resumed his recitation from 
    where he had got to, and no one noticed that he had forgotten anything 
    except those who were Haafiz (i.e., had memorised the entire Qur'aan). 

    Majmoo’ al-Fataawa, 
    21/410, 411. 

    And Allah knows best.