What to say upon finish reading the Qur’an?
Here is a benefit on what to say when you finish reciting the Quran. Unfortunately, the innovation of reading (صدق الله العظيم) has become very widespread. The Sunnah is the following:

Aisha radiallahu anha said:
ما جلس رسول الله – صلى الله عليه وعلى آله وسلم – مجلسا ، ولا تلى قرآن ، ولا صلى صلاة ، إلا ختم ذلك بكلمات ، قالت : فقلت : يا رسول الله أراك ما تجلس مجلسا ولا تتلو قرآنا ، ولا تصلى صلاة ، إلا ختمت بهؤلاء الكلمات قال : نعم ، من قال خيرا ختم له طابع على ذلك الخير ، ومن قال شرا ، كن له كفارة : سبحانك وبحمدك ، لا إله إلا أنت ، أستغفرك وأتوب إليك 
The Messenger of Allah sallahu alayhi wa salam did not sit in a sitting, or recite Quran, or pray a prayer except he completed it with those words. So I said: Oh Messenger of Allah, I see that you do not sit in a gathering or recite Quran or pray a prayer except you complete with the following words. He said: Yes. Whoever says good, it will complete it for him and will be a seal for that good. And whoever said evil, it will be an expiation for him:
سبحانك وبحمدك ، لا إله إلا أنت ، أستغفرك وأتوب إليك 
O Allah, You are free from every imperfection; praise be to You. I testify that there is no true god except You; I ask Your Pardon and turn to You in repentance
[Reported by Nasai in Amal ul-Yawm wa Laylah and graded Saheeh by Shaikh Wad’iee in Saheeh Musnad no. 1598]
Imam Nasaai rahimahullah placed the chapter:
ما ختم تلاوة القرآن
“What to complete the recitation of the Quran with [i.e. what to say]”
[Sunan al-Kubra (6/84)]

So this is what should be read when one is finished reciting the Quran and not 

(صدق الله العظيم) 
Hassan ibn ‘Attiyah rahimahullah spoke the truth when he said:
 ما ابتدع قوم بدعة في دينهم إلا نزع الله من سنتهم مثلها
“A people do not innovate in their religion an innovation, except Allah will remove from their Sunnah something similar”
[Reported by ad-Daarami no. 99 and the chain is Saheeh]
So let us replace the innovation by returning to the Sunnah. 
Allah says:
لَّقَدْ كَانَ لَكُمْ فِى رَسُولِ اللَّهِ أُسْوَةٌ حَسَنَةٌ لِّمَن كَانَ يَرْجُو اللَّهَ وَالْيَوْمَ الاٌّخِرَ وَذَكَرَ اللَّهَ كَثِيراً 
Indeed in the Messenger of Allah (Muhammad ) you have a good example to follow for him who hopes in (the Meeting with) Allah and the Last Day and remembers Allah much
[33:21]
Translated by
Faisal Ibn Abdul Qaadir Ibn Hassan

Abu Sulaymaan

Click below:

the-day-your-lord-comes-shaykh-ibn-uthaymeen

http://www.islamfromthestart.com/2015/05/100-quranic-words.html

Tafsir of Surah al-‘Asr: Imam al-Sa’di – http://wp.me/p2NmFj-Xe