Ruling on reciting dhikr without focus of mind and reflection
Question

Will the Muslim be rewarded for reciting dhikr without focus of mind (reciting dhikr automatically)? Will he be rewarded for that, such as reciting tahlil (La ilaha illa Allah) or istighfar (Astaghfirullah), but without focus of mind? Will he receive the reward in full, as mentioned in the hadiths that speak of dhikr?
Praise be to Allah.Firstly:
What the Muslim should do is remember Allah, may He be exalted, properly, so that he will reap the benefits of dhikr and achieve its objectives, which cannot be achieved unless the verbal dhikr is accompanied by dhikr in the heart, for it is not sufficient for the person to simply move his lips and tongue in dhikr.
Allah, may He be exalted, says (interpretation of the meaning):
{The believers are only those who, when Allah is mentioned, their hearts become fearful, and when His verses are recited to them, it increases them in faith; and upon their Lord they rely} [al-Anfal 8:2].
The benefits of dhikr – namely fear of Allah and increased faith – cannot be attained except through reflection and contemplation.
Shaykh ‘Abd ar-Rahman as-Sa‘di (may Allah have mercy on him) said:
{are only those who, when Allah is mentioned, their hearts become fearful} that is, they are filled with fear and awe, and that fear of Allah (st) dictates that they should refrain from that which is prohibited. Fear of Allah (st) is one of the greatest signs that restrain one from committing sin.
{and when His verses are recited to them, it increases them in faith}, the reason being that they listen to them with presence of mind, contemplating the meaning, and as a result of that their faith increases, because contemplation is one of the actions of the heart, and it is inevitable that they will learn a meaning that they did not know, or they will be reminded of something that they had forgotten, or it will make their hearts inclined towards good and make them long for the reward of their Lord, or will make them fear His punishment, or they will be deterred from sin. All of these are things that increase one in faith."(Tafsir as-Sa‘di, p. 315).
Being content merely to recite dhikr verbally, without reflection in the heart, will not lead to the hoped-for benefits of dhikr as it should be done, and it will be an action that falls short.
Ibn al-Qayyim (may Allah have mercy on him) said:
Dhikr with focus and reflection will increase a person’s knowledge of Allah and love of Him; it will make him feel shy before Him and prompt fear of His punishment, and it will make him realise that Allah is constantly watching him, which will deter him from falling short in doing acts of worship or being careless in committing sins and doing bad deeds.
Dhikr that is only verbal will not lead to any of these benefits, and if it does lead to any of that, it will be lacking."(Al-Wabil as-Sayyib ( p. 221).
Secondly:
If the Muslim falls short and only recites dhikr verbally, will he be rewarded?
It was said that yes, he will be rewarded as befits his deed, for moving the tongue with words remembering Allah is a righteous deed with which the tongue is occupied, and it is a verbal act of worship. If he reflects in his heart on what his tongue is uttering, that is good, otherwise his reward will be commensurate with his action.
However, there will inevitably be some sort of reflection in the heart on what he is saying, even if it is not perfect, and he will think of what he is saying to some extent. Hence he will choose a supplication (du‘a’), for example, in one situation, and he will choose istighfar or pure dhikr in other situations, and so on, and Allah has ordained reward for every action.
An-Nawawi (may Allah have mercy on him) said:
Al-Qadi ‘Iyad (may Allah have mercy on him) said: dhikr or remembrance of Allah, may He be exalted, is of two types: dhikr in the heart and dhikr on the tongue… As for dhikr on the tongue or purely verbal dhikr, it is the least type of dhikr, but it is still of great value, as mentioned in the hadiths."(Sharh Sahih Muslim  17/15).
Al-Hafiz Ibn Hajar (may Allah have mercy on him) said:
If dhikr is recited verbally only, the one who utters it will be rewarded.
It is not stipulated that he should focus on the meaning, but it is stipulated that he should not intend its meaning in a wrong way.
If, in addition to uttering the words, he focuses on them in his heart, that is better.
If, in addition to that, he bears in mind the meaning of the words and what they contain of venerating Allah, may He be exalted, and denying that He has any shortcomings, that is even better."(Fath al-Bari  11/209).
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
With regard to dhikr, people are at four levels:

Dhikr in the heart and on the tongue; this is what is enjoined.
Dhikr in the heart only. If the person is unable to speak, that is fine, but if he is able to speak, then he has failed to do what is better.
Dhikr on the tongue only. In this case the person is keeping his tongue moist with the remembrance of Allah, as is mentioned in the story of the person in whom the angels found nothing good to his credit except that he kept moving his tongue in remembrance of Allah. Allah, may He be exalted, says (in the hadith qudsi): “I am with My slave so long as he remembers Me and his lips move in remembrance of Me.”
When there is neither kind of dhikr. This is the state of the losers."(Majmu‘ Fatawa 10/566).

For more information, please see the answers to questions no. 72826 and 235993 .
And Allah knows best.