He has repented from not praying or giving zakah; does he have to make them up?
Question

I am from a Muslim background, but I never used to offer the obligatory prayers and even when I tried to pray once, I did not do it right. In other words I did not prepare to do it in the proper manner. I ask Allah to forgive me. I heard that the one who does not pray is a disbeliever and is not a Muslim, but whoever offers the five daily prayers, or one or two of them and omits the rest, is regarded as a Muslim. Also, I did not pay zakah on my wealth, but for at least two years I have completed the fast of Ramadan, and I intend to continue doing so. I want to learn how to pray and make it part of my life, along with other acts of worship.
Is it obligatory for me to pay zakah for all these many years (when I did not pay it), and to make up the days that I did not fast at the time when I was not praying?
Please note that I have now reached the age of thirty-one years; perhaps you will understand that this may cause me a great deal of hardship; to ward off that hardship, can I start over? Will Allah forgive me if I do that?
Praise be to Allah.Firstly: 
We praise Allah for having blessed you with guidance and enabled you to repent sincerely from the state of shortcomings and negligence you had been in. We ask Allah to complete His blessing upon you and to make you steadfast in adhering to the straight path. 
With regard to making up acts of worship that you did not do, such as prayer and fasting, there are two scholarly opinions. Some of the scholars think that it is obligatory to make them up; this is the view of the majority. 
Some scholars do not think that the one who did not pray is obliged to make up the prayers that he missed, based on the view that he was a disbeliever (at the time when he was not praying), so when he repents he is in effect becoming Muslim, which erases all sins that came before it. 
Other scholars do not think that the one who deliberately did not pray has to make up those prayers, regardless of whether it is said that he was a disbeliever at that time or not, because the text only speaks of the one who is excused because he fell asleep and missed the prayer or he forgot it. 
The correct view on the issue of one who fails to fast or pray with no excuse is that he does not have to make up what he did not do; rather what he must do is repent, and pray and fast regularly from now on. It is mustahabb for him to do a lot of naafil (supererogatory) acts of worship, fasting and prayers, in the hope that Allah will accept his repentance. 
Requiring the one who has repented to make up what he has missed makes it very hard to repent and puts people off it. But the one who repents must do a lot of righteous deeds, because Allah, may He be exalted, says (interpretation of the meaning):
“And verily, I am indeed Forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them, (till his death)” [Ta-Ha 20:82]. 
See also the answer to question no. 91411  
Secondly: 
If we determine that the one who does not pray is a disbeliever, then in the case of one who does not give zakah as well as not praying, one of the following must apply: 
1.Either he stopped praying before zakah became due from him. In this case, if he repents from not praying, then he does not have to make up the zakah that he did not pay, because one of the conditions of zakah being obligatory is that one should be a Muslim, but this person was not a Muslim at the time when zakah became due from him, so he does not have to make it up;
2.Or he stopped praying after zakah became due from him. In this case there is a difference of opinion among the scholars (may Allah have mercy on them) as to whether he is obliged to make it up after repentance or not. 
Ibn Qudaamah (may Allah have mercy on him) said:
If he apostatized before one year had passed, and the year [for paying zakah] ended when he was still an apostate, then he does not have to pay zakah, because being Muslim is one of the conditions of zakah being obligatory. The fact that he was not Muslim for part of the year means that zakah is waived, because being Muslim is one of the conditions of zakah being obligatory, along with ownership and the nisaab (minimum threshold). If he comes back to Islam before the year has ended, the year (for zakah)starts anew, for the reasons we have mentioned. Ahmad said: If an apostate becomes Muslim again, and one year has passed since his wealth came into his possession, then it is his, and he does not have to pay zakah until one full year passes after he became a Muslim again, because he was not required to give zakah (when he was not a Muslim). 
But if he apostatised after one year had passed, zakah is not waived in his case. This is the view of ash-Shaafa‘i. Abu Haneefah said: It is waived, because one of the conditions of zakah is having the intention (niyyah) to give it. So it is waived in the case of apostasy, just as prayer is also waived. 
We say that it is what is due from wealth, so it is not waived in the case of apostasy, just as debts are not waived.
End quote from al-Mughni (2/348-349) 
It says in al-Mawsoo‘ah al-Fiqhiyyah (23/234-235):
With regard to the apostate, if he apostatized after one year had passed since his wealth reached the nisaab (minimum threshold), then zakah is not waived according to the Shaafa‘is and Hanbalis, because it is something that is due from wealth, so it is not waived in the case of apostasy, just as debts are not waived. The ruler should take it from his wealth just as zakah is taken from the Muslim who withholds it. Then if he becomes Muslim again after that, he does not have to pay zakah again. 
The Hanafis are of the view that in the case of apostasy, zakah on wealth owned by the apostate before he apostatised is waived, because one of its conditions is that one should have the intention (niyyah) of paying zakah at the time of giving it. The intention is an act of worship, but he is a disbeliever, so it does not count; therefore it is waived in the case of apostasy, just as prayer is also waived; this also applies on zakah on produce of the land. 
But if he apostatised before one year had passed since his wealth reached the nisaab (minimum threshold), then it is not proven that he is obliged to pay it, according to the majority of Hanafis and Hanbalis; this is also one view among the Shaafa‘is. End quote. 
To sum up with regard to zakah: 
If he failed to pay any of it when he was still praying, and it was only because he was lazy or miserly, then he must pay what he did not pay of zakah at that time. The debt owed to Allah is more deserving of being paid off. 
But if he did not pay zakah at the same time as he did not pray, then he must repent to Allah from that, give up this negligence, and start doing righteous deeds, in the hope that Allah may forgive him and expiate what he did in the past. Allah, may He be exalted, says (interpretation of the meaning):
“Say to those who have disbelieved, if they cease (from disbelief) their past will be forgiven. But if they return (thereto), then the examples of those (punished) before them have already preceded (as a warning)” [al-Anfaal 8:38].
The Prophet (blessings and peace of Allah be upon him) said to ‘Amr ibn al-‘Aas (may Allah be pleased with him), when he swore allegiance to him and pledged to follow Islam: “Do you not know that Islam erases whatever came before it.” 
All of this applies if he stopped praying altogether. But if he used to pray sometimes and did not pray sometimes, then we have previously stated on our website that we favour the view that he is not to be regarded as a disbeliever in this case; as he was not a disbeliever, he is definitely obliged to pay what he failed to pay of zakah, because it is a debt that he owes, and this obligation cannot be discharged except by paying it. 
This applies if he knows that he possessed wealth that reached the nisaab at that time and one (hijri) year had passed since acquiring it, but he did not pay zakah on it. But if he did not have any wealth, or he had wealth but it did not reach the nisaab, or it reached the nisaab but one year did not pass since then, then he is not obliged to pay zakah on any of it. 
A similar case is if he is not sure whether he possessed the wealth or whether it reached the nisaab; the basic principle is that he does not owe anything. 
With regard to prayer, there is a considerable difference of scholarly opinion in cases such as this. The view of the majority is also that he must make up what he missed, and undoubtedly this is more prudent and more likely to be on the safe side. 
We ask Allah to help us and you to obey Him and to protect us from the evils of our own selves, for He is Munificent, Most Generous. 
The following are some answers having to do with encouragement to offer the prayers and have patience in doing so. Please see questions no. 99139 and 47123 
And Allah knows best.