If there's no permanent ladder or stairs leading to the attic, you may be able to simply lay the cable across the rafters.

"Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.".

National Electrical Code

Chapter 3 Wiring Methods and Materials

334.23 In Accessible Attics. The installation of cable in accessible attics or roof spaces shall also comply with 320.23.

Article 320 Armored Cable: Type AC

320.23 In Accessible Attics. Type AC cables in accessible attics or roof spaces shall be installed as specified in 320.23(A) and (B).

(A) Where Run Across the Top of Floor Joists. Where run across the top of floor joists, or within 2.1 m (7 ft) of floor or floor joists across the face of rafters or studding, in attics and roof spaces that are accessible, the cable shall be protected by substantial guard strips that are at least as high as the cable. Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.

(B) Cable Installed Parallel to Framing Members. Where the cable is installed parallel to the sides of rafters, studs, or floor joists, neither guard strips nor running boards shall be required, and the installation shall also comply with 300.4(D).

Article 300.4(D) says that if you do attach the cable to the ridge beam, you'll have to keep it 1 1/4" away from either edge.

Article 300 Wiring Methods

300.4 Protection Against Physical Damage. Where subject to physical damage, conductors shall be protected.

(D) Cables and Raceways Parallel to Framing Members and Furring Strips. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm (1 1⁄4 in.) from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm (1⁄16 in.) thick.

It was not particularly clear from your posting just what this 1x4 is in the wall. If it was flat to the back side of the drywall surface and went up at an angle in one direction and down at an angle in the other direction then this is a big problem. In this case this 1x4 is a cross brace installed in notches across a batch of studs. It's purpose is to triangulate with the studs to stiffen the building structure and keep things square. This would have been something that should not have been cut. Instead you should have moved your hole over and patched over the first hole.