shiekh there is a brother who is in his late 20s ,but he is not fineinaclly stable and is planing on getting married to a sister and but he doesnt knows if he can take care of her so is he sinful if he ends process of the marriage , and starts to fast , because of the hadiths of the prophet

He's not sinful unless he's going to fall into that which is forbidden. However, he knows his situation best. We recommend that he gets married and that he dedicates his time and effort into making enough money, insha'Allah, to provide for himself and the sister. He should ask Allah and depend on Allah; with his wife, insha'Allah, comes rizq.