His father gave him more than he gave to him; is this regarded as riba?
Question

                I pay for some household goods for my father from my own pocket, say 150 riyals, with the intention of it being an act of charity, but sometimes my father gives me 200 riyals and says, “Don’t pay from your pocket.” If he gives me 200 riyals is this regarded as riba?.
Praise be to Allah.
    Honouring one’s parents is one of the greatest means of 
    attaining Paradise. What a great loss it is if a person’s parents reach old 
    age and he does not make honouring them a means of entering Paradise. The 
    Prophet  (peace and blessings of Allaah be upon him) said: “May his nose 
    be rubbed in the dust, may his nose be rubbed in the dust, may his nose be 
    rubbed in the dust.” It was said: “Who, O Messenger of Allaah?” He said: 
    “The one who lives to see his parents reach old age, one or both of them, 
    and he does not enter Paradise because of them.” Narrated by Muslim, 2551. 
    See also questions no. 22782 and 
    5326. 

    One of the ways of charity through which a person may seek 
    reward with Allaah is to spend on his parents and take care of them with his 
    own wealth. By doing that you will have the reward of doing charity in sha 
    Allaah. The Prophet  (peace and blessings of Allaah be upon him) said: 
    “If a person spends on his parents, seeking reward, it will be an act of 
    charity for him.” Narrated by al-Bukhaari, 55. 

    With regard to your question, if you buy goods for your 
    father worth 150 riyals and he gives you 200, there is no sin in that, as he 
    has voluntarily given you more than you paid. There is no riba in this case. 
    Riba can hardly be imagined between a son and his father, and both of you 
    are doing well in sha Allah. You wanted to give him the value of the goods 
    and he wanted to give you something extra. We ask Allaah to reward you both 
    and to bless you both in your wealth.