Objection 1. It would seem that solicitude does not belong to prudence. For solicitude implies disquiet, wherefore Isidore says (Etym. x) that "a solicitous man is a restless man." Now motion belongs chiefly to the appetitive power: wherefore solicitude does also. But prudence is not in the appetitive power, but in the reason, as stated above (Article 1). Therefore solicitude does not belong to prudence.
Objection 2. Further, the certainty of truth seems opposed to solicitude, wherefore it is related (1 Samuel 9:20) that Samuel said to Saul: "As for the asses which were lost three days ago, be not solicitous, because they are found." Now the certainty of truth belongs to prudence, since it is an intellectual virtue. Therefore solicitude is in opposition to prudence rather than belonging to it.
Objection 3. Further, the Philosopher says (Ethic. iv, 3) the "magnanimous man is slow and leisurely." Now slowness is contrary to solicitude. Since then prudence is not opposed to magnanimity, for "good is not opposed to good," as stated in the Predicaments (viii) it would seem that solicitude does not belong to prudence.
On the contrary, It is written (1 Peter 4:7): "Be prudent... and watch in prayers." But watchfulness is the same as solicitude. Therefore solicitude belongs to prudence.
I answer that, According to Isidore (Etym. x), a man is said to be solicitous through being shrewd [solers] and alert [citus], in so far as a man through a certain shrewdness of mind is on the alert to do whatever has to be done. Now this belongs to prudence, whose chief act is a command about what has been already counselled and judged in matters of action. Hence the Philosopher says (Ethic. vi, 9) that "one should be quick in carrying out the counsel taken, but slow in taking counsel." Hence it is that solicitude belongs properly to prudence, and for this reason Augustine says (De Morib. Eccl. xxiv) that "prudence keeps most careful watch and ward, lest by degrees we be deceived unawares by evil counsel."
Reply to Objection 1. Movement belongs to the appetitive power as to the principle of movement, in accordance however, with the direction and command of reason, wherein solicitude consists.
Reply to Objection 2. According to the Philosopher (Ethic. i, 3), "equal certainty should not be sought in all things, but in each matter according to its proper mode." And since the matter of prudence is the contingent singulars about which are human actions, the certainty of prudence cannot be so great as to be devoid of all solicitude.
Reply to Objection 3. The magnanimous man is said to be "slow and leisurely" not because he is solicitous about nothing, but because he is not over-solicitous about many things, and is trustful in matters where he ought to have trust, and is not over-solicitous about them: for over-much fear and distrust are the cause of over-solicitude, since fear makes us take counsel, as stated above (I-II, 44, 2) when we were treating of the passion of fear.
Source: Summa Theologica (New Advent)