If it keeps happening after you've installed a known good inner tube, make sure that your installation procedure is correct ( you're not damaging the inner tube when you're installing it), and the tire is free of anything that could damage the inner tube.

For example, I once had to enlarge the hole on the tire to fit a larger valve, and one metal shaving found its way to the bottom of the tire.

If it keeps happening after you've installed a known good inner tube, make sure that your installation procedure is correct (you're not damaging the inner tube when you're installing it), and the tire is free of anything that could damage the inner tube.

For example, I once had to enlarge the hole on the rim to fit a larger valve, and one metal shaving found its way to the bottom of the tire.