Is it allowable to take small notes, circle some words, underline some words on mushaf (Book of Quran)? It could be helpful while learning tajweed. Is it considered disrespectful?
No, it's not disrespectful.
The holy Quran was written by Sahabah (radya Allah 'anhum) to keep it from distortion. And we have "copies" (mushafs) because we (most of us) don't memorize the whole Quran, so we need a way to be able to read and learn it, there is no problem with putting marks while learning.
Also there are many mushafs that come with tafseer (e.g, I have a copy which has tafseer Ibn Katheer every page with it's tafseer beside it). And, better example, there are mushafs where letters are colored according to the tajweed situation of that letter, they're very helpful in fact (there are electronic programs that has so, as well), and nobody objected to it.
I would compare it to the idea that reading Quran while walking, is not disrespectful.
Anyway, I (personally) think it's better to make that on a personal mushaf, i.e, one which only you read from, in order to avoid any possible misunderstanding.
EDIT: I searched and found this fatwa by Abdullah Ibn Jebreen, which confirms what came above:
Q: Some Quran teachers leave notes and marks with pencils on their mushafs or their students' mushafs to notify them about their mistakes. For example they underline Ghunnah (غنة) places and the like of reciting rules, they do that after the recitation is complete. So is it permitted to write similar things on mushafs?
A: I see it's OK to put these notes and marks for the reasons mentioned in the question, it's OK to put them on the margin, on the footnote, or even between the lines, in case these notes were symbols and marks similar to stop and tajweed marks that are normally in mushafs. If these notes were small, written with pencils so they can be erased when no longer of use, then it's OK to put them. It's only not allowed to put on mushaf what doesn't belong to Quran if there was danger that the reader will think these things are part of Quran, or are describing it (and they originally don't). If there no such danger, then we see no problem putting these notes and marks when needed. And Allah knows best. And Salla Allah 'ala Muhammad wa 'ala alihi wa sahbihi wa sallam.
Abullah bin Abdulrahman Ibn Jebreen
Qur'an vs. Moshaf vs. pages of the moshaf
First you must distinguish between the Qur'an as the word of Allah () revealed to the prophet () and transmitted orally via narrator chains until this day. And the moshaf which is written a copy of the content of the Qur'an. Beside this the ruling that apply on a moshaf and pages of the moshaf can differ in fiqh.
What is certainly prohibited
It is certainly not allowed to write anything that is unrelated to Qur'an on a moshaf. For example writing your name or words of wisdom etc.. Here applies the ruling of respect, as nothing can be set equal or higher than the words of Allah that are parts of a moshaf.
Opinions on writing Qur'an related explanations or marks on the moshaf
As to what is related to the Qur'an like tafseer, recitation marks etc. there are basically two different opinions on this topic:
- Allowing to write the meanings of the words of the Qur'an and it's tafsir at the margins of the moshaf.
Some evidences can be found in al-Muwatta' here and here the same narration was also compiled in some of the Sunan and Sahih Muslim. And show that it is allowed to write in between the letters of the moshaf.
Imam al-Baji also quoted a statement of imam Malik in his al-Muntaqa a commentary of al-Muwatta':
If in the following I'm translating from Arabic without explicitly quoting a source, then these translations are of my own take them carefully!
وروى أشهب عن الإمام مالك قوله :
" لا يزاد في المصاحف ، وأما مصاحف صغارٍ يَتعلم فيها الصبيان وألواحهم فلا بأس بذلك "
Ashhab narrated from Malik that he said: "It is not allowed to add to the moshafs, but as for the moshafs for little learners in which they learn and their boards it is not harmful to do so".
Note that imam Malik is considered among the strongest opponents on adding to moshaf something that is different from what the sahabah have done. So he prefers the text and letters to stay as written originally.
And you may find in hanafi sources:
إن كتب القرآن وتفسير كل حرف وترجمته جاز
If one wrote down the Qur'an and the tafseer of each letter and its translation it is permissible. (Source islamqa #147968)
And -in the same fatwa source- it said Shafi'i scholars are considering touching a moshaf which is printed or written beside a tafsir for a person who has no wudu' as permissible.
- It is not allowed to write tafsir or whatever in the moshaf copies.
Among those who opposed writing anything inside the moshaf you may find: the sahabi 'Abdullah ibn Mas'ud who according to the fatwa above (from islmaqa) removed a line he found in a moshaf and he used to say:
جَرِّدُوا القرآن ولا تلبسوا به ما ليس منه
Keep the Qur'an as is (as it was revealed) and don't add to it what is not part of it.
Ibn Mas'ud however is known to have been teaching the Qur'an by using tafsir recitations (synonyms of words for those who were unable to pronounce the original words in Arabic).
Ibraheem an-Nakha'i and 'Ata' ibn abi Rabah were also among those who considered adding to moshaf what is not part of it as illegal.
In the same fatwa you may read the following quotes from shafi'i sources. Here a statement on how to show respect for the Qur'an by abu 'Abdillah al-Halimi:
" ومنها : أن لا يخلط في المصحف ما ليس من القرآن بالقرآن ، كعدد الآيات ، والسجدات ، والعشرات ، والوقوف ، واختلاف القراءات ، ومعاني الآيات "
Among these (ways): Not to mix in a moshaf what is not part of the Qur'an with the Qur'an (text), like the number of a verse, or sajdah, or ten verses (marks) or waqf (pausing) or diffrences of qira'aat or the meaning of verses.
Note that most of the above actually appear in almost all moshafs we have in hand these days.
And al Jurjani said:
من المذموم كتابة تفسير كلمات القرآن بين أسطره
It is (disrespectful and strongly) disliked to write the meaning of the words of the Qur'an between the lines.
The Permanent Committee for Scholarly Research and Ifta even gave a fatwa following the above view and advising a person not to write inside a moshaf and use separated pages and papers instead in which one may refer to the verses.
Nevertheless most scholars consider the first view as stronger as the prohibition of mixing Qur'an texts with content that is not part of the Qur'an was an issue in the early days of Islam. Nevertheless those people who excelled the Qur'an used to add to the Qur'an what was not part of it as the hadith above beside other narrations show. So the reasons fro prohibition or dislike are the necessity to have a standard text. And this doesn't apply anymore which is a conclusion already scholars such as a-Zayla'i came to and he widely explained this based on the statement of 'Abdullah ibn Mas'ud.
Therefore you may find in this fatwa on islamweb #135535 a permission to write inside or at the margins of the Qur'an whatever is related to it with the advise to use a pencil as it would be easy to remove once the notes are no more needed.
If you think it is "disrespectful" you are giving the quran powers beyond material and that is a major shirk. The only thing that matters is your intentions, if your intentions are good and you are reading and learning and not cluttering etc, I don't see any problems.