In Part One, I gave an overview of the penitential practices of bodily mortification (particularly, use of the hair shirt or biblical sackcloth). Here I provide the relevant Scriptures (RSV), so that Catholics may substantiate the biblical nature of their practices.
Use of Sackcloth as a Sign of Repentance or Penitence
Matthew 11:21 Woe to you, Chora’zin! woe to you, Beth-sa’ida! for if the mighty works done in you had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes. (cf. Lk 10:13)
2 Kings 19:1 When King Hezeki’ah heard it, he rent his clothes, and covered himself with sackcloth, . . . (cf. 1 Kgs 20:31; Is 37:1-2)
Nehemiah 9:1-2 . . . the people of Israel were assembled with fasting and in sackcloth, and with earth upon their heads.  And the Israelites . . . confessed their sins and the iniquities of their fathers. (cf. Ps 69:10-11)
Jeremiah 4:8 For this gird you with sackcloth, lament and wail; for the fierce anger of the LORD has not turned back from us. (cf. Is 32:11)
Jeremiah 6:26 O daughter of my people, gird on sackcloth, and roll in ashes; . . . (cf. Ezek 7:18; Jonah 3:5)
Use of Sackcloth in Conjunction with Prayer and Supplication
1 Chronicles 21:16-17 . . . Then David and the elders, clothed in sackcloth, fell upon their faces.  And David said to God, “Was it not I who gave command to number the people? It is I who have sinned and done very wickedly. But these sheep, what have they done? Let thy hand, I pray thee, O LORD my God, be against me and against my father’s house; but let not the plague be upon thy people.”
Psalm 35:13 But I, when they were sick — I wore sackcloth, I afflicted myself with fasting. I prayed with head bowed on my bosom, (cf. 30:8, 10-11; Dan 9:3)
Jonah 3:7-9 And he made proclamation and published through Nin’eveh, “By the decree of the king and his nobles: Let neither man nor beast, herd nor flock, taste anything; let them not feed, or drink water,  but let man and beast be covered with sackcloth, and let them cry mightily to God; yea, let every one turn from his evil way and from the violence which is in his hands.  Who knows, God may yet repent and turn from his fierce anger, so that we perish not?”
Use of Sackcloth in Mourning
2 Samuel 3:31 Then David said to Jo’ab and to all the people who were with him, “Rend your clothes, and gird on sackcloth, and mourn before Abner.” . . . (cf. 21:10; Gen 37:34; 2 Kgs 6:30; Is 58:5)
Isaiah 22:12 In that day the Lord GOD of hosts called to weeping and mourning, to baldness and girding with sackcloth; (cf. 15:3; Jer 48:37; 49:3; Lam 2:10; Ezek 27:31; Joel 1:8, 13; Amos 8:10)
Deliberate Self-Infliction of Deprivation for Spiritual / Intercessory Purposes
Exodus 17:11 Whenever Moses held up his hand, Israel prevailed; and whenever he lowered his hand, Am’alek prevailed.
Ezra 9:3, 5-6 When I heard this, I rent my garments and my mantle, and pulled hair from my head and beard, and sat appalled. . . .  And at the evening sacrifice I rose from my fasting, with my garments and my mantle rent, and fell upon my knees and spread out my hands to the LORD my God,  saying: “O my God, I am ashamed and blush to lift my face to thee, my God, for our iniquities have risen higher than our heads, and our guilt has mounted up to the heavens.” (cf. Jer 41:5; 48:37)
Ezekiel 4:4-8 “Then lie upon your left side, and I will lay the punishment of the house of Israel upon you; for the number of the days that you lie upon it, you shall bear their punishment.  For I assign to you a number of days, three hundred and ninety days, equal to the number of the years of their punishment; so long shall you bear the punishment of the house of Israel.  And when you have completed these, you shall lie down a second time, but on your right side, and bear the punishment of the house of Judah; forty days I assign you, a day for each year.  And you shall set your face toward the siege of Jerusalem, with your arm bared; and you shall prophesy against the city.  And, behold, I will put cords upon you, so that you cannot turn from one side to the other, till you have completed the days of your siege.”
Luke 2:36-37 And there was a prophetess, Anna, . . .  . . . She did not depart from the temple, worshiping with fasting and prayer night and day.
1 Corinthians 9:27 but I pommel my body and subdue it, lest after preaching to others I myself should be disqualified.
Fasting is also obviously an example of bodily deprivation for a spiritual purpose. See: Ex 34:28 and Deut 9:9 (Moses went forty days without even water); Deut 9:18 (Moses again fasts forty days without “bread” or “water” on behalf of the Israelites, after the sin of the idolatry of the golden calf); 1 Sam 30:12 (three days without water); 1 Sam 31:13 (seven days); 2 Sam 1:12; 1 Ki 19:8 (forty days); 1 Chron 10:12 (seven days); 2 Chron 20:3; Ezra 8:21-23; 10:6; Neh 1:4; 9:1; Esther 4:3; 4:16 (three days without food and water); 9:31; Ps 69:10 (“humbled my soul with fasting”); Ps 109:24 (“My knees are weak through fasting; my body has become gaunt”); Jer 36:9; Dan 6:18; Joel 1:14; 2:12, 15; Jon 3:5, 7; Zech 7:3, 5; 8:19; Matt 4:2 (Jesus’ forty days of fasting in the wilderness); Matt 6:16-18; 9:14-15 (cf. Mk 2:18-20; Lk 5:33-35; 18:12); Lk 7:33 (cf. Matt 11:18; Lk 1:15); Acts 13:2-3; 14:23.