The severity of his leg pain caused him to resign his commission in 1862, after the Battle of Seven Pines.
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At the Battle of Seven Pines, however, Sumner's initiative in sending reinforcing troops across the dangerously rain-swollen Chickahominy River prevented a Union disaster.
Rains was wounded during the Battle of Seven Pines, and was singled out by Maj. Gen. Daniel Harvey Hill for a successful flanking maneuver that turned the tide of battle in favor of the Confederates.
Commissioned as a major general on September 19, he served in Northern Virginia as a divisional and "wing" commander, and fought in the Battle of Seven Pines near Richmond during the Peninsula Campaign.
The 71st participated in the Peninsular Campaign of 1862, although it isn't clear whether Wistar was actually present; at the Battle of Seven Pines (May 31 and June 1) the regiment was led by its major, and during the Seven Days Battles (June 30 and July 1) commanded by its lieutenant colonel.