Commercial Fixed Wing
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Situational Awareness; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Environment - Non Weather Related; Human Factors; Procedure
Normal (very early) departure.  We taxied out; ran checklists; lined up for takeoff; when I added power; we got the takeoff configuration warning horn.  We both saw immediately the flaps were not set. I notified tower we needed to exit the runway.  Exited the runway at the first taxiway.  I don't think our ground speed got above 25-40 (?) knots.  Set the flaps; re-ran the before takeoff checklist; notified the Tower ready; and completed the flight normally.Haven't been flying as much as normal.  First flight; very early morning.  Possible distraction(s). This is a humbling event.  I don't think I've done it in X0 years of flying.  There was nothing specific that I remember; but something interfered with our regular routine or 'flow'.   I did the 'after start' checklist and missed it; and we both did the 'before takeoff' checklist aloud and missed it.   I thought I was checking the position and the indicators carefully; but obviously I need to be more stringent; and will be in the future.
When cleared for takeoff; and starting to line up and advancing throttles; a configuration aural warning activated because the flaps were in the up position. Neither of us realized the flaps in the incorrect position before taking the runway and I immediately took control of the aircraft and returned the thrust levers to the idle position; disconnected the auto throttle and cleared the runway; never exceeding 10-12 knots (still at taxi speed). Once clear of the runway; I commanded the flap lever to 1 and first officer moved lever to 1 and we got the green light. Ran the entire before takeoff checklist again and was cleared back onto runway for an uneventful takeoff and climbout.I had completed a 3 day trip late the previous night and this was an early XA30 departure time with minimum required rest. I stayed at the hotel and was interrupted in my sleep routine at around midnight by a noisy neighbor conducting a phone call in the room next to mine. Maybe I wasn't fully rested and still a little groggy.  My expectation was that the flap lever was placed to 1 after engine start and I was used to that routine so I didn't register that the flaps were not in the correct position. This was the first time this has occurred for me.Only suggestion is to double and triple check all items; especially configuration items; and to use the crew concept better.
Air carrier flight crew reported not setting the flaps resulting in a takeoff configuration warning on takeoff roll.