SQL & PL/SQL

i am working on a banking system ,where i am implementing the function of taking money from one account and add it to another account so i write a procedure to do the following:
1 update the first account(reduce x)
2 update the second account(add x)
so what is the safest way to call that procedure???
( i call it from when-button-press trigger then i do commit to make sure that the two actions were completed before doing commit)

transfer(:value);
commit;