Is it permissible to offer money to a person on the condition that he does a good deed?
Question

                Is it permissible to offer money to a person on the condition that he does a good deed ? For example, can I say to a Muslim uncle, I will give you 500 Dirhams if you grow and keep a beard ?.
Praise be to Allah.It seems that there is nothing wrong with 
    doing that. Allaah has enjoined certain actions upon His slaves, and has promised a great reward in this world for doing them, so as to encourage 
    people to do them. Allaah says (interpretation of the meaning): 
“And whosoever fears Allaah and keeps his 
    duty to Him, He will make a way for him to get out (from every difficulty).
 And He will provide him from (sources) he never could imagine”
[al-Talaaq 65:2-3] 
The Prophet  (peace and blessings of 
    Allaah be upon him) said: “Whoever would like his provision in this world to be increased and his life span to be extended, let him uphold the 
    ties of kinship.” Narrated by al-Bukhaari, 5986; Muslim, 2557. 
As a way of encouraging righteous deeds, the 
    Prophet  (peace and blessings of Allaah be upon him) gave permission for the one who killed a kaafir on the battelefield to take his spoils. 
It was narrated that Abu Qutaadah (may Allaah 
    be pleased with him) said: The Messenger of Allaah  (peace and blessings of Allaah be upon him) said, during the year of Hunayn: “Whoever 
    kills an enemy and has proof of that will have his spoils.”
Narrated by al-Bukhaari, 2973; Muslim, 1751. 
“Spoils” here refers to the money, luggage, 
    clothing and weapons that a fighter has with him. 
And the scholars regarded it as permissible 
    to offer prizes for memorizing soorahs from the Qur’aan or ahaadeeth, or for winning a contest of knowledge. 
The scholars of the Standing Committee were 
    asked: 
What is the ruling on receiving prizes for 
    Qur’aan memorization contests? 
They replied: 
There is nothing wrong with that, and there is no difference between men and women in this 
    regard. 
Fataawa al-Lajnah al-Daa’imah, 
    4/126 
This has to do with giving and offering: it 
    is permissible to offer and give money to one who lets his beard grow or does other things required by sharee’ah. 
But with regard to the one who takes that 
    money: if he let his beard grow in order to take the prize, then he will not be rewarded for his action, but if the prize motivated him to fulfil 
    the command of Allaah, or if he started because of the prize and then changed his intention after that and adhered to (following the ruling), then 
    he will be rewarded for that in which his intention was sound, and it will not matter that at first he was doing it for the prize. 
It was narrated from Anas that a man asked 
    the Prophet  (peace and blessings of Allaah be upon him) for sheep between two mountains and he gave them to him, then he went to his people 
    and said, “O my people, become Muslims, for by Allaah Muhammad gives generously and he does not fear poverty.” 
Anas said: People would become Muslim only 
    for worldly gains, but as soon as they became Muslim Islam became dearer to them than this world and everything in it. 
Narrated by Muslim, 2312. 
Al-Nawawi said: 
This is how it appears in most copies: “fa ma 
    yuslim (as soon as [they] became Muslim).” In some copies it says “fa ma yumsi (before the day ended).” Both are correct. The first means that 
    shortly after they became Muslim, Islam became dearer to them, i.e., at first they professed Islam for worldly purposes, with no sound intention 
    in their hearts, then by the blessing of the Prophet  (peace and blessings of Allaah be upon him) and the light of Islam, their hearts were 
    soon opened to true faith which took root in their hearts, and then Islam became dearer to them than this world and everything in it. 
Sharh Muslim, 
    15/72, 73. 
And Allaah knows best.