The Scottish Confession (easy to find through google), written in 1560 by a group of Reformed theologians that included John Knox, says this with respect to assurance of salvation and the good works that believers do:
Chapter 12 - Faith in the Holy Spirit
This our faith and its assurance do not proceed from flesh and blood, that is to say, from natural powers within us, but are the inspiration of the Holy Spirit; whom we confess to be God, equal with the Father and with his Son, who sanctifies us, and brings us into all truth by his own working, without whom we should remain forever enemies to God and ignorant of his Son, Christ Jesus. For by nature we are so dead, so blind, and so perverse, that neither can we feel when we are pricked, see the light when it shines, nor assent to the will of God when it is revealed, unless the Spirit of the Lord Jesus quicken that which is dead, remove the darkness from our minds, and bow our stubborn hearts to the obedience of his blessed will. And so, as we confess that God the Father created us when we were not, as his Son our Lord Jesus redeemed us when we were enemies to him, so also do we confess that the Holy Spirit sanctifies and regenerates us, without respect to any merit proceeding from us, be it before or after our regeneration. To put this even more plainly; as we willingly disclaim any honor and glory from our own creation and redemption, so do we willingly also for our regeneration and sanctification; for by ourselves we are not capable of thinking one good thought, but he who has begun the work in us alone continues us in it, to the praise and glory of his undeserved grace.
Chapter 13 - The Cause of Good Works
The cause of good works, we confess, is not our free will, but the Spirit of the Lord Jesus, who dwells in our hearts by true faith, brings forth such works as God has prepared for us to walk in. For we most boldly affirm that it is blasphemy to say that Christ Jesus abides in the hearts of those in whom is no spirit of sanctification. Therefore we do not hesitate to affirm that murderers, oppressors, cruel persecutors, adulterers, filthy persons, idolaters, drunkards, thieves, and all workers of iniquity, have neither true faith nor anything of the Spirit of the Lord Jesus, so long as they obstinately continue in wickedness.
For as soon as the Spirit of the Lord Jesus, whom God's elect children receive by true faith, takes possession of the heart of any man, so soon does he regenerate and renew him, so that he begins to hate what before he loved, and to love what he hated before. Thence comes that continual battle which is between the flesh and Spirit in God's children, while the flesh and the natural man, being corrupt, lust for things pleasant and delightful to themselves, are envious in adversity and proud in prosperity, and every moment prone and ready to offend the majesty of God. But the Spirit of God, who bears witness to our spirit that we are the sons of God, makes us resist filthy pleasures and groan in God's presence for deliverance from this bondage of corruption, and finally to triumph over sin so that it does not reign in our mortal bodies.
Carnal men do not share this conflict since they do not have God's Spirit, but they readily follow and obey sin and feel no regrets, since they act as the devil and their corrupt nature urge. But the sons of God, as already said, fight against sin, sob and mourn when they find themselves tempted to do evil, and if they fall, they rise again with earnest and unfeigned repentance. They do these things, not by their own power, but by the power of the Lord Jesus, apart from whom they can do nothing.