Define end-effector pose by point and vector

Hi all, I am using a UR10 with Moveit! for motion planning (move group interface C++). I want to align my end-effector with a vector in space. I read a lot about quaternions and rotation in 3d space, but at the moment I struggle to find out the best way to do this. I have a given point (x,y,z) and a given vector for orientation (a,b,c), how can I set a target pose for the end-effector? Tried to use a geometry_msg but it needs a point and a quaternion. Also tried to calculate a quaternion between the current vector and the goal vector using cross product etc. but therefore I would need the vector of the current pose and I struggled to find it out -.- Does anybody know a clean solution for my problem? Thank you very much in advance! Hannes