The complete hadith is as following:
Narrated Abu Hurairah (radiallahu ta’ala anhu): Allah’s Messenger (sallallahu alayhi wa sallam) said,
“When the month of Ramadan comes, the gates of Paradise are opened and
the gates of (Hell) Fire are closed, and the devils are chained.”
[Sahih al Bukhaari #3277]
There are many types of Shayateen with varying levels of wickedness.
Those who reside in the toilets are known as Khubuth:
“Anas reported that when the Messenger of Allah (salallahu alayhi
wassalam) entered the privy he would say, "In the name of Allah. O
Allah! I seek refuge in you from male (khubuth) and female
(khabaa’ith) noxious beings (devils)." (Bukhari & Muslim)
Those who disturb us in the prayer are called Khinzaab:
Narrated Uthman ibn Abul'As: Uthman came to Allah's Messenger (salallahu alayhi wassalam) and said:
Allah's Messenger, the Satan intervenes between me and my prayer and
my reciting of the Qur'an and he confounds me. Thereupon Allah's
Messenger (peace be upon him) said: “That is (the doing of the Satan)
who is known as Khinzab, and when you perceive its effect, seek
refuge with Allah from it and spit three times to your left.” I did
that and Allah dispelled that from me. (Sahih Muslim, Ahmad, Abu
Dawood)
The one who are more wicked than the Shaytaan is called Maarid:
“And to guard against every rebellious devil (Shaytaan maarid).”
[Suran al-Saaffaat (37):7]
The most strong amongst them is called 'Ifreet:
“(Sulaymaan) said (to his own men): "O Chiefs! Which of you can bring
me her throne before they come to me in submission?" An 'Ifreet
(strong one) from the jinn said: "I will bring it to you before you
rise from your place (council). And verily, I am indeed strong and
trustworthy for such work." One with whom was knowledge of the
Scripture said: "I will bring it to you within the twinkling of an
eye!" Then when (Sulaymaan) saw it placed firmly before him he said:
"This is by the grace of my Lord! to test me whether I am grateful or
ungrateful! And if any is grateful truly his gratitude is (a gain) for
his own soul; but if any is ungrateful truly my Lord is Free of All
Needs Supreme in Honor!" [Surah al-Naml (27): 38-40]
And there are more types of shayateen like these.
Coming to the question,
Shakyh Abdur-Rahmaan bin Naasir as-Sa’di (rahimuhullaah) said in the chapter “Baab us-Siyaam” (Chapter of Fasting) in his book Minhaj as Saalikeen (translated to English):
As the Gates of Jannah are being opened at the same time the Gates of
Jahannam are being closed.The Shayaateen are in levels, Iblis being at
the top and then the Khabith next and the small shayateen. Iblis and
the Khabith shayateen (May Allaahs Curse be upon them until The Hour),
the Maarid (sick ones) are locked up but the small shayateen are not
locked up; hence why you see some small evil in Ramadhaan. The strong
shayateen called maarid, they are also being locked up and chained in
the month of Ramadhaan.
Hence, these small shayateen try to trap us and we choose to fall into it and sin. May Allah save us from that.
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