The conditions are as follows:
1. Islam;
So the prayers of the disbelievers are invalid, and they are not accepted. Likewise all the practices they do. Allah Subhanahu wa Ta'ala says: "It is not proper for the polytheists to prosper the mosques of Allah, while they admit that they themselves are disbelievers. These are the people whose labors are in vain, and they are eternally in Hell.” (At-Taubah:17)
2. Reasonable;
So the prayer is not obligatory for the madman, as the words of the Prophet sallallaahu alaihi wasallam: "There are three groups of people whose pens have been lifted from him (not given the burden of shari'ah), namely; a person who sleeps until he wakes up, a child until he reaches puberty and a madman until he recovers." (Narrated by Abu Dawud and others, authentic hadith)
3. Baligh;
So, it is not obligatory for a child to pray until he reaches puberty, as mentioned in the hadith above. However, the young child should be ordered to pray from the age of seven years and his prayer is sunnah for him, as the Prophet sallallaahu 'alaihi wasallam said: "Order children to pray when they are seven years old, and when they are ten years old, beat them if they don't do it." (Narrated by Abu Dawud and others, authentic hadith)
4. Holy From Minor Hadats and Big Hadats;
Small hadats is not in a state of ablution and big hadats is not bathing from junub.
The proof is the word of Allah Subhanahu wa Ta'ala: "O you who believe, when you want to pray, then wash your face and your hands up to the elbows, and wipe your head and (wash) your feet up to the ankles, and if you are junub then take a shower." (Al-Maidah: 6)
The Prophet sallallaahu 'alaihi wasallam said:
"Allah will not accept prayer without purification." (HR. Muslim)
5. Sacred Body, Clothes and Place for Prayer;
As for the evidence regarding the purity of the body is the words of the Prophet sallallaahu 'alaihi wasallam against women who bleed istihadhah: "Wash the blood that is on your body then perform the prayer." (Narrated by Al-Bukhari and Muslim)
As for the evidence about the supposed purity of clothing, namely the word of Allah Subhanahu wa Ta'ala: "And your clothes, then you should purify them." (Al-Muddatstsir: 4)
As for the argument about the necessity of a sacred place of prayer, namely the hadith of Abu Hurairah radhiyallahu anhu, he said: "A village man stood up and he urinated in the mosque of the Messenger of Allah (peace and blessings of Allah be upon him) so that the crowds stood up to beat him, so the Messenger of Allah (sallallaahu alaihi wasallam) said, 'Leave him alone and pour a bucket of water into his urinal, indeed you have been sent bringing ease and not sent with hardship.” (Narrated by Al-Bukhari).
As for the argument about the necessity of a sacred place of prayer, namely the hadith of Abu Hurairah radhiyallahu anhu, he said: "A village man stood up and he urinated in the mosque of the Messenger of Allah (peace and blessings of Allah be upon him) so that the crowds stood up to beat him, so the Messenger of Allah (sallallaahu alaihi wasallam) said, 'Leave him alone and pour a bucket of water into his urinal, indeed you have been sent bringing ease and not sent with hardship.” (Narrated by Al-Bukhari).
6. Enter Prayer Times;
Prayers are not obligatory unless the time has come, and it is not legal to pray before the time has come. This is based on the words of Allah Subhanahu wa Ta'ala: "Indeed, prayer is an obligation whose time is determined for those who believe." (An-Nisa': 103)
That is, that prayer has a certain time. And the angel Gabriel also came down, to teach the Prophet sallallaahu alaihi wasallam about prayer times. Jibril led him at the beginning of time and at the end of time, then he said to the Prophet sallallaahu 'alaihi wasallam: "In between the two is the time for prayer."
7. Cover aurat;
This is based on the words of Allah Subhanahu wa Ta'ala: "O son of Adam, wear your beautiful clothes in every (entering) mosque." (Al-A'raf: 31)
What is meant by beautiful clothes are those that cover the genitals. The scholars agree that covering the nakedness is a condition for the validity of prayer, and whoever prays without covering the nakedness, while he is able to cover it, then his prayer is invalid.
8. Intention;
This is based on the words of the Prophet sallallaahu 'alaihi wasallam: "Indeed, all deeds depend on the intention, and indeed everyone will get (reply) according to his intention." (Narrated by Al-Bukhari and Muslim)
9. Facing Qibla;
This is based on the words of Allah Subhanahu wa Ta'ala: "Indeed We (often) see your face looking up at the sky, then We will surely turn you to the Qibla that you like. Turn your face towards the Grand Mosque. And wherever you are, turn your face towards it." (Al-Baqarah: 144)