(Abraham) staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God…Now it was not written for his sake alone, that (righteousness) was imputed to him, but for us also, to whom it shall be imputed, if we believe on Him that raised up Jesus our Lord from the dead _Romans 4:20, 23-24

I ought to be afraid of presumption, but it cannot be presumptuous to believe God’s word. I ought to be afraid of saying, “Peace, peace, where there is no peace;” but if peace comes to me through the word of Christ, I need never be suspicious of it, let it be as profound as it may. I may doubt myself; I may go further, I may despair of self, but I must not doubt the Lord. If He has said, “Trust in Me, believe in Me, and thou shalt be saved;” if I believe in Him, it is no presumption to know that I am saved. If He has declared that he that believeth in Him is justified from all things from which he could not be justified by the law of Moses; if I have believed in Him, I am justified from all my sins. There is far more presumption in doubting the Lord than there ever can be in trusting Him. Faith is no more than God’s due, it ought never to be looked at as too daring. If I believe in Jesus I have no right to say, “I hope I am saved,” for that implies a doubt of God’s declaration that the believer is saved. I have no right to say, “I sometimes think I am safe.” I am so undoubtedly if I believe in Jesus. It is no matter of opinion, but a matter of certainty. There is nothing in this world about which a man may be so sure as about his own salvation, because other things come to us by the evidence of our own fallible senses, or by the testimony of men who may be mistaken; but the fact that the believer is saved is sealed to us by the testimony of God Himself, who cannot lie. When the Scripture says plainly, “He that believeth and is baptized shall be saved,” I, having believed, and having been baptized, ought not to question the divine declaration, but should be as sure that, if I have believed, I am saved, as I am sure that I exist. This assurance is attainable, and should be the common condition of the believer. Yet has it often happened, I say, that an anxiety, which was commendable in its outset, has ended in a censurable unbelief.~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/1033.cfm