I have heard it said many times in religious/spiritual and/or typical conversation that "there is more to know than that which is written [in the bible]." Is this comment scripturally inspired? If so where can the comment or its inspiration be found in scripture?
Try the very last verse of the book of John:
Jesus did many other things as well. If every one of them were written down, I suppose that even the whole world would not have room for the books that would be written.
— New International Version
Beside that, it is obvious that much of the minutia of daily life is missing from the Bible.
From Orthodox catechism
2 John 1:12
I have much to write to you, but I do not want to use paper and ink. Instead, I hope to visit you and talk with you face to face, so that our joy may be complete.
Consequently, faith comes from hearing the message, and the message is heard through the word of Christ.
Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.
2 Timothy 2:2
And the things you have heard me say in the presence of many witnesses entrust to reliable men who will also be qualified to teach others.
1 Corinthians 11:2
Now I commend you because you remember me in everything and maintain the traditions even as I delivered them to you.
2 Thessalonians 2:15
So then, brothers, stand firm and hold to the traditions that you were taught by us, either by our spoken word or by our letter.
In Holy Tradition of Orthodoxy the valid interpretation of the Scripture can be made only by Holy Spirit, through saints. Other than their interpretations, are just opinions. According to this approach, inside Orthodox church cannot exist 2 different confessions, both them valid, because Holy Spirit cannot separate or contradict Himself.
1 Corinthians 3:16
Don't you know that you yourselves are God's temple and that God's Spirit lives in you?
The Bible is a collection of books established inside Holy Tradition of the Orthodox church. These books where collected by the disciples of the apostles, transmitted to the disciples of the disciples, in so on, for almost 4 centuries. In this time a multitude of apocriphal writtings, came up, and recognition of the autentic books became a problem inside the church. The canon of the Bible were proposed to by the saint Athanasios the Great (+373), saint Gregory the Teologian (+389), saint Amphilochios (+403). Because only temples of the Holy Spirit could recognize which are the books inspirated by Holy Spirit, the holy fathers approved in ecumenic councils (Laodicea, Carthage) which books can be included in Holy Scripture. (http://symeon-anthony.info/BibleCanon/CanonicalBibleBooks.htm)
The Canon of the Holy Bible, was only one canon from a multitude of other canons. (http://theocacna.tripod.com/canonsaa.htm) Saint Atanasios the Great which proposed the canon of Holy Scripture most closed by the one accepted today wasn't an adept of "Sola Scriptura", because he wrote for the church another book called: "The life of Saint Anthony the Great", which was his spiritual father. And the canon 46 of council from Cathage states one of the practice of the apostolic church:
The passions of the Martyrs may be read when their anniversary days are celebrated.
In Orthodox Tradition the life of the martyrs and the teachings of holy fathers of the egyptian desert or sinai are another precious tresures similar to the Bible. The Bible can be seen as the THEORY, and the life of the martyrs and desert fathers can be seen as the PRACTICE.
New International Version (NIV)
5 Trust in the Lord with all your heart and lean not on your own understanding;
This tells me we really don't know anything and that there is much more than what is written.
I remember working with children with disabilities and thinking this is what it must be like for God working with us, saying to himself they can't see or understand all these things but I will help them.
The scripture does in fact speak plainly on this issue, and the fact that so many are ignoring it concerns me greatly. The scriptures say - 1 Corinthians 4:6
"Now these things, brethren, I have figuratively transferred to myself and Apollos for your sakes, that you may learn in us not to think beyond what is written, that none of you may be puffed up on behalf of one against the other."
And 2nd Corinthians 1:13-14 goes on to further illustrate this point.
"For we are not writing any other things to you than what you read or understand. Now I trust you will understand, even to the end (as also you have understood us in part), that we are your boast as you also are ours, in the day of the Lord Jesus."
The moment you get outside of what is written, you fall into the trap of the enemy, sound doctrine is dismissed and all manner of teachings pop up, inspired by men and NOT the Living God. Scripture provides us with the context to view all doctrine, and once you get outside of it and allow so-called individual revelation to enter in you set yourself up for all manner of heretical teachings, such as the so called Gospel of Mary, or Gospel of Judas. Scripture is the boundary, if its not written it is not acceptable. Scripture will never contradict scripture.