What happened to the Scripture of Ibraaheem and the Zaboor of Dawood (peace be upon them)?
Question

                Were the Zaboor and the Scripture of Ibraaheem distorted?
Praise be to Allah.Firstly:
Allah, may He be exalted, revealed a Scripture to Ibraaheem, as He, may He be exalted, said (interpretation of the meaning):
“Indeed, this is in the former scriptures,
The scriptures of Abraham and Moses”
[al-A‘laa 87:18-19].
Allah, may He be glorified and exalted, has told us in His holy Book about some of what was in the Scripture of Ibraaheem (peace be upon him). Allah, may He be exalted, says (interpretation of the meaning):
“Or has he not been informed of what was in the scriptures of Moses
And [of] Abraham, who fulfilled [his obligations] – 
That no bearer of burdens will bear the burden of another
And that there is not for man except that [good] for which he strives
And that his effort is going to be seen
Then he will be recompensed for it with the fullest recompense… ”
[an-Najm 53:36-40 … until the end of the soorah].
Similar to that is the well-known verses at the end of Soorat al-A‘laa, which are quoted above.
What is required of us is only to believe in general terms in the Scriptures that Allah, may He be exalted, sent down to His Prophet Moosaa (peace be upon him), and to believe in whatever is proven to us to be sound through the revelation sent to the Prophet Muhammad (blessings and peace of Allah be upon him), in which there are lessons and exhortations. As for anything more than that, such as details of what those Scriptures contained, we are not obliged to know it and we have no way of knowing it or finding out about its details. Trying to find out about that is taking on something that cannot be proven, and we have no need of that according to the teachings of our religion, for Allah has perfected our religion for us and is pleased with Islam for us as our religion.
We know of no religious text that suggests that the Scripture of Ibraaheem (peace be upon him) is still extant, or that the knowledge contained therein reached any of the people of Islam in such a manner that it can be proven and relied upon.
What appears to be the case is that its knowledge was abrogated a long time ago and was lost to people.
In fact, this is applicable to the books of the Children of Israel, namely the Torah and the Gospel; there is no longer anything that can be authenticated in that which is extant among them, except for that which is confirmed by Islamic religious texts. As for everything other than that, the most that can be said is that we neither believe in it nor disbelieve in it.
If this is the case with regard to the books of the Children of Israel, despite the large numbers of people who venerate them, pay attention to them and refer to them, then it is even more likely that this is the case with regard to the Scripture of Ibraaheem (peace be upon him). The most can be said about what is extant among people of that, that is attributed to the Scripture of Ibraaheem (peace be upon him), is that it is like the Scriptures and Books of the Children of Israel: we neither believe in it nor disbelieve in it.
For more information, see the answers to questions no. 199116 and 126004.
Secondly:
With regard to the Zaboor of Dawood (peace be upon him), it is the Book that Allah revealed to him. Allah, may He be exalted, says (interpretation of the meaning): “And your Lord is most knowing of whoever is in the heavens and the earth. And We have made some of the prophets exceed others [in various ways], and to David We gave the book [of Psalms [Zaboor]]” [al-Israa’ 17:55].
The word zaboor refers to something written. Tafseer at-Tabari (6/17).
At-Taahir said:
It is the name for the collected sayings of Daawood (peace be upon him) – some of which are words that were revealed to him, and some are words with which he was inspired, words of supplication and conversing with Allah. It is the book that is known nowadays as the Book of Psalms in the Old Testament.
End quote from at-Tahreer wa’t-Tanweer (15/138).
The scholars have stated that the Zaboor of Dawood contained words of praise and glorification of Allah, may He be exalted; it did not contain any rulings on what is lawful and what is prohibited (halaal and haraam), or on shares of inheritance or hudood punishments. See Tafseer at-Tabari (14/625).
Al-Qurtubi said: The Zaboor is the book of Dawood. It contained one hundred and fifty chapters, in which there were no rulings or statements of what is lawful and what is prohibited; rather it was words of wisdom and exhortation.
There are references to the contents of the Zaboor and the Scripture of Ibraaheem in some reports which are not proven.
In the hadith of Abu Dharr (may Allah be pleased with him) it says:
I said: O Messenger of Allah, what was the Scripture of Ibraaheem?
He said: “It was all proverbs, such as:
O powerful and arrogant king, I did not appoint you to pile up worldly gains one on top of another; rather I appointed you to avert from Me the supplication of the one who has been wronged, for I do not reject it even if it comes from a disbeliever.
Every rational individual, unless he loses his mind, must have certain times: a time in which he converses with his Lord, a time in which he takes stock of himself, a time in which he reflects upon the creation of Allah, and a time in which he focuses on meeting his need for food and drink.
Every rational individual should not focus his mind except on three things: seeking provision for the hereafter [by doing righteous deeds], working to earn a living, and finding pleasure in something that is not prohibited.
The intelligent man should have insight into the era in which he lives, focus on his own affairs and guard his tongue.
Whoever regards his words as being among his deeds will speak little and will only speak about what concerns him.”
I [Abu Dharr] said: O Messenger of Allah, what was the Scripture of Moosa?
He said: “It was all exhortations:
I am astounded by the one who is certain of death, for how can he rejoice?
I am astounded by the one who is certain of the Fire, for how can he laugh?
I am astounded by the one who is certain of the divine decree, for how can he strive too hard?
I am astounded by the one who sees this world and its vicissitudes, for how can he be at ease with it?
I am astounded by the one who is certain of the reckoning tomorrow, for how can he not strive?”
This hadith was narrated by Ibn Hibbaan (361) and others. Al-Arnaa’oot said in his comments on the book of Ibn Hibbaan: Its isnad is da‘eef jiddan (very weak). The same was stated by Shaykh al-Albaani in ad-Da‘eefah. See Tafseer Ibn Katheer (2/472).
What we have stated above about the Scripture of Ibraaheem (peace be upon him) with regard to how authentic it is and the extent to which we may trust its contents, we may also state with regard to the Zaboor, because we have no report to indicate that it has survived. Whatever has been transmitted of it via the People of the Book comes under the same ruling as the Israa’eeliyyaat (reports narrated from Jewish sources), which are of three categories:

Acceptable: this refers to that which is known to be sound due to its having been soundly narrated from the Messenger of Allah (blessings and peace of Allah be upon him).
That concerning which no verdict is given: this refers to that for which it cannot be known whether it is valid or false. It is permissible to narrate reports of this category for the purpose of exhortation and admonition, but we do not believe that it is either sound or false, in compliance with the command of the Messenger of Allah (blessings and peace of Allah be upon him).
Rejected: this refers to that which is known to be false, and it is not appropriate to believe it, accept it or narrate it.

For more information, please see the answers to questions no. 265035 and 22289.
And Allah knows best.