St. Seraphim of Sarov: Do not Judge your Neighbor

We must not Judge anyone, even if with our own eyes we have seen someone sinning, or walking in transgression of God's commandments. For according to the word of God: "Judge not, that ye be not judged" (Matt 7:1), and again: "Who art thou that judgest another man's servant? To his own master he standeth of falleth; yea, he shall be holden up: for God is able to make him stand" (Rom 14:4).
It is much better always to bring to mind these words of the Apostle: "Let him that thinkest he standeth take heed lest he fall" (1 Cor 10:12).
For we do not know how long we may remain in virtue, as says the Prophet who attained to knowledge of this matter by experience: "In my prosperity I said, I shall never be moved. Thou didst hide Thy face, and I am troubled" (Ps 29:7-8).
+St. Seraphim of Sarov, from Spiritual Instructions, Instruction XX Do not Judge your Neighbor, in Little Russian Philokalia, Vol 1: St. Seraphim.