«وَضَبْطُ كِتَابٍ: وَهُوَ صِيَانَتُهُ لَدَيْهِ مُنْذُ سَمِعَ فِيهِ وَصَحَّحَهُ إِلَى أَنْ يُؤَدِّيَ مِنْهُ»
Precision through a book means protecting a verified written record from the time of reception and correction until it is used to transmit the report.
The relevant copy must remain reliable: unverified changes, scribal confusion, altered pages, or unauthorized interventions must not corrupt its contents. Possessing a notebook is not enough; the actual narration must be taken from an accurately maintained record.
Dabt al-sadr and dabt al-kitab are two legitimate routes to the same goal: preservation of the report. One transmitter may excel in memorization, another in safeguarding his authenticated notes. Complete precision is judged in the mode by which that narrator actually transmits.