Discipline is an indication of love. It's in the Bible, Hebrews 12:5-11, NIV. "My son, do not make light of the Lord's discipline, and do not lose heart when he rebukes you, because the Lord disciplines those he loves, and he punishes everyone he accepts as a son. Endure hardship as discipline; God is treating you as sons. For what son is not disciplined by his father? If you are not disciplined (and everyone undergoes discipline), then you are illegitimate children and not true sons. Moreover, we have all had human fathers who disciplined us and we respected them for it. How much more should we submit to the Father of our spirits and live! Our fathers disciplined us for a little while as they thought best; but God disciplines us for our good, that we may share in his holiness. No discipline seems pleasant at the time, but painful. Later on, however, it produces a harvest of righteousness and peace for those who have been trained by it."
Discipline is an expression of parental love. It's in the Bible, Proverbs 13:24, TLB. "If you refuse to discipline your son, it proves you don't love him; for if you love him, you will be prompt to punish him."
Discipline when children are young averts bigger trouble later. It's in the Bible, Proverbs 19:18, TLB. "Discipline your son in his early years while there is hope. If you don't you will ruin his life."