It has been said that the jinn only attack those with low Imaan. Is this true?

I would not agree that the jinn only attack people with low imaan or faith. It may be more often among them because their belief is weak, but it also affects those whose Imaan may be fine. As the Prophet (ﷺ) could be affected by magic; and the element of magic has to do with the jinn, therefore, it may happen to any person. However, it does tend to frequent among those who are deviated, and whose faith is weak etc. One should not have this false idea that if my faith is strong, nothing can affect me. It can affect you as a test. Thus, the Prophet (ﷺ) taught us how to protect ourselves.

The Prophet (ﷺ) said that the Shaytaan inspires man to evil and calls him to evil. There are times when he has control over man's heart and can find out, by Allah’s decree, what a person intends to do of good or evil. There are also times when the angel has control over a person’s heart. He makes him incline towards good and calls him to good. These are things that Allah has enabled them to do, i.e., He has enabled the two companions, the jinn-companion and the angel-companion, to do these things. Even the Prophet (ﷺ) had a Shaytaan with him, his constant companion (qareen) from among the jinn, as stated in the hadeeth which says, that the Prophet (ﷺ) said:

“There is no one among you but he has with him a constant companion (qareen) from among the jinn and a constant companion from among the angels.” They said, “You too, O Messenger of Allah?” He said, “Me too, but Allah has helped me against him (the devil-companion) and he has become Muslim, so he does not tell me to do anything but good.”[1]

The point is that every man has with him a companion from among the angels and a companion from among the shayateen. The believer suppresses his shaytaan by obeying Allah and adhering steadfastly to His religion, so he humiliates his shaytaan until he becomes weak and unable to stop the believer from doing good, or making him fall into evil, except what Allah wills. The sinner, by his disobedience and evil actions, gives his shaytaan the strength to make him do evil and encourages him to do evil, and discourages him from doing good. The believer has to fear Allah and strive against his shaytaan by obeying Allah and His Messenger (ﷺ), and seeking refuge with Allah from the Shaytaan. He should strive to help his angel by obeying Allah and His Messenger (ﷺ) and heeding the commands of Allah.

The jinn live on this earth where we do. They are mostly to be found in ruins and unclean places like bathrooms, dunghills, garbage dumps and graveyards. Hence the Prophet (ﷺ) taught us to take precautions when entering such places, by reciting the adhkaar (prayers) prescribed by Islam. One of these was reported by Anas ibn Maalik (رضى الله عنه), who said: “When the Messenger of Allaah (ﷺ) entered the toilet, he would say, ‘Allaahumma innee a’oodhubika min al-khubuthi wa’l-khabaa’ith (O Allah, I seek refuge with You from the evil ones, male and female).’”[2]

Al-Khattaabi, explained that khubuth is the plural of khabeeth (evil or dirty – masculine form), and khabaa’ith is the plural of khabeethah (evil or dirty – feminine form), and that what is meant is male and female Shayaateen.

Some jinns are Muslim and some are Kaafir, because Allaah tells us in Surah al-Jinn, that some of the jinn said; (interpretation of the meaning):

“‘And some of us are Muslims, and of us some are al-qaasitoon (disbelievers – those who have deviated from the Right Path). And whosoever has embraced Islam, and then such have sought the Right Path. And as for the qaasitoon, they shall be firewood for Hell.’”[3]

Since the jinn can see us while we cannot see them, the Prophet (ﷺ) taught us many ways to protect ourselves from their harm, such as seeking refuge in Allah from the accursed Shaytaan, reciting Soorat al-Falaq and Soorat al-Naas (the last two Soorahs of the Qur’an), and reciting the words taught by Allah in the Qur’an in Surah al-Mu’minoon;

وَقُل رَّبِّ أَعُوذُ بِكَ مِنۡ هَمَزَٲتِ ٱلشَّيَـٰطِينِ (٩٧

 And say, "My Lord, I seek refuge in You from the incitements of the devils,

 وَأَعُوذُ بِكَ رَبِّ أَن يَحۡضُرُونِ (٩٨

And I seek refuge in You, my Lord, lest they be present with me."[4]

Saying, Bismillaah (in the Name of Allah) before entering one’s home, before eating or drinking, and before having intercourse will also keep the Shaytaan from entering the house or partaking with a person in his food, drink and sexual activity. Similarly, mentioning the name of Allah before entering the toilet or taking off one’s clothes will prevent the jinn from seeing a person’s ‘awrah or harming him, as the Prophet (ﷺ) said, “To put a barrier that will prevent the jinn from seeing the ‘awrah of the sons of Aadam, let any one of you say ‘Bismillaah’ when entering the toilet.”[5]

Strength of faith and religion in general will also prevent the jinn from harming a person, so much so, that if they were to fight, the one who has faith would win. ‘Abd-Allaah ibn Mas’ood (رضى الله عنه) said: “A man from among the Companions of Muhammad (ﷺ) met a man from among the jinn. They wrestled, and the human knocked down the jinn. The human said to him, ‘You look small and skinny to me, and your forearms look like the front paws of a dog. Do all the jinn look like this, or only you?’ He said, ‘No, by Allah, among them I am strong, but let us wrestle again, and if you defeat me I will teach you something that will do you good.’ The human said, ‘Fine.’ He said, ‘Recite, ‘Allah! None has the right to be worshipped but He, the Ever-living, the One Who sustains and protects all that exists…’ [Aayat al-Kursi – al-Baqarah 2:255 – interpretation of the meaning]. The human said, ‘Fine.’ He said, ‘You will never recite this in your house, but the Shaytaan will come out of it like a donkey breaking wind, and he will never come back in until the next morning.’”[6]

Source:

http://islamqa.com/en/ref/2340/jinn

http://islamqa.com/en/ref/8214/jinn

References:

[1]Muslim, hadith no. 2814.

[2]Bukhari, 142 and Muslim, 375.

[3]Quran, 72:14-15.

[4]Quran, 23:97-98.

[5] Jaami’ al-Tirmidhi, 551; Saheeh al-Jaami’, 3611.

[6]al-Daarimi, 3247