All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Since your father has taken the entire amount of 100, then he has borrowed this amount from you, and there is no harm on you in taking it back when he gives it back to you.
It should be noted here that even if the loan contract is void (prohibited), this does not make it forbidden for the person to take his capital money (the 100 in your case). Therefore, avoid these doubts and whispers.
If your father is insolvent, then you should drop this debt from him and not demand him to give you back the money, especially if you don't need it.
Among the acts of kindness is to keep good ties with the parents by means of giving them money, even if they don’t need it; let alone if they need it. The children are obliged to spend on their parents if they are poor. Ibn Qudaamah said:
“The scholars have agreed in a consensus that the sustenance of the poor parents who have no source of income and who have no money is an obligation on their child." [End of quote]
For more benefit, please refer to Fataawa 320281, 379468, 332464.
Allah knows best.